Table of Contents

Index to Financial Statements

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

For fiscal year ended December 31, 2008

OR

COMMISSION FILE NO. 1-6622

WASHINGTON REAL ESTATE INVESTMENT TRUST

(Exact name of registrant as specified in its charter)

6110 EXECUTIVE BOULEVARD, SUITE 800, ROCKVILLE, MARYLAND 20852

(Address of principal executive office) (Zip code)

Registrant’s telephone number, including area code: (301) 984-9400

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    YES  x    NO  ¨

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    YES  ¨    NO  x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or such shorter period that the registrant was required to file such reports) and (2) has been subject to such filing requirements for the past ninety (90) days.    YES  x    NO  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the registrant’s knowledge in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definition of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer  x            Accelerated filer  ¨            Non-accelerated filer  ¨            Smaller reporting company  ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).    YES  ¨    NO  x

As of June 30, 2008, the aggregate market value of such shares held by non-affiliates of the registrant was approximately $1,470,494,526 (based on the closing price of the stock on June 30, 2008).

As of February 26, 2009, 52,996,595 common shares were outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of our definitive Proxy Statement relating to the 2009 Annual Meeting of Shareholders, to be filed with the Securities and Exchange Commission, are incorporated by reference in Part III, Items 10-14 of this Annual Report on Form 10-K as indicated herein.

Table of Contents

Index to Financial Statements

WASHINGTON REAL ESTATE INVESTMENT TRUST

2008 FORM 10-K ANNUAL REPORT

INDEX

2

Table of Contents

Index to Financial Statements

PART I

WRIT Overview

Washington Real Estate Investment Trust (“we” or “WRIT”) is a self-administered, self-managed, equity real estate investment trust (“REIT”) successor to a trust organized in 1960. Our business consists of the ownership and operation of income-producing real properties in the greater Washington metro region. We own a diversified portfolio of office buildings, medical office buildings, industrial/flex properties, multifamily buildings and retail centers.

We believe that we qualify as a REIT under Sections 856-860 of the Internal Revenue Code and intend to continue to qualify as such. To maintain our status as a REIT, we are required to distribute 90% of our ordinary taxable income to our shareholders. When selling properties, we have the option of (a) reinvesting the sale price of properties sold, allowing for a deferral of income taxes on the sale, (b) paying out capital gains to the shareholders with no tax to us or (c) treating the capital gains as having been distributed to our shareholders, paying the tax on the gain deemed distributed and allocating the tax paid as a credit to our shareholders.

Over the last five years, dividends paid per share have been $1.72 for 2008, $1.68 for 2007, $1.64 for 2006, $1.60 for 2005 and $1.55 for 2004.

Our geographic focus is based on two principles:

We consider markets to be local if they can be reached from Washington within two hours by car. While we have historically focused most of our investments in the greater Washington metro region, in order to maximize acquisition opportunities we will consider investments within the two-hour radius described above. We also may consider opportunities to duplicate our Washington-focused approach in other geographic markets which meet the criteria described above.

All of our trustees, officers and employees live and work in the greater Washington metro region and a majority of our officers average over 20 years of experience in this region.

This section includes or refers to certain forward-looking statements. You should refer to the explanation of the qualifications and limitations on such forward-looking statements beginning on page 50.

The Greater Washington Metro Area Economy

In 2008, the Washington metro region experienced positive job growth, an increase in gross regional product (“GRP”), and the lowest unemployment rate among the major markets in the nation. However, the national economic recession has still negatively affected our region. Current projections indicate that the Washington metro region added 26,000 new jobs in 2008 as one of the few national markets with positive job growth in 2008. The professional and business services, leisure and hospitality, health care and federal/state government sectors led job growth in the region. According to the Center for Regional Analysis (“CRA”) at George Mason University, the Washington area’s GRP in 2008 is estimated to have increased 2.5%, which is similar to the experience of the 2001-2002 economic slowdown. Approximately one-third of the area’s GRP was generated by the federal government. The region’s unemployment rate was 4.1% at October 2008, up a full 1.0% as compared to 2007, but still remains the lowest rate among all of the nation’s largest metro areas. In addition, the region’s unemployment rate is well below the national average of 6.5% in October 2008.

Growth in the Washington metro region is expected to be modest compared to past years. According to CRA, The Washington Leading Index, which forecasts area economic performance over the next 18 months, was 107.0, as of September 2008, below the 108.9 achieved in September 2007, but above the 20-year average of 102.1. GRP for the Washington metro region is forecasted to increase by only 1.5% in 2009 and gradually improve going forward into 2010. Job growth in the region is forecasted to soften in 2009 and increase in 2010, adding 24,000 and 37,000 new jobs, respectively, compared to the long-term 15-year average of 53,000.

3

Table of Contents

Index to Financial Statements

Greater Washington Metro Region Real Estate Markets

Despite softening economic conditions, we believe the greater Washington metro region remains one of the top performing real estate markets in the nation. The region experienced a decrease in investment sales in excess of 70% from 2007 levels. However, the Association of Foreign Investors in Real Estate (AFIRE) has publicized that it now considers Washington, DC as the top global city for real estate investment. The area’s economy has translated into stronger relative real estate market performance in each of our segments, compared to other national metropolitan regions, as reported by Delta Associates / Transwestern Commercial Services (“Delta”), a national full service real estate firm that provides market research and evaluation services for commercial property types including office, industrial, retail and apartments. Nevertheless, we believe the potential exists in the current economic environment for downward pressure on rents in 2009. Market statistics and information from Delta are set forth below:

Office and Medical Office Sectors

Retail Sector

Multifamily Sector

Industrial/Flex Sector

4

Table of Contents

Index to Financial Statements

Our Portfolio

As of December 31, 2008, we owned a diversified portfolio of 93 properties consisting of 28 office properties, 17 medical office properties, 14 retail centers, 12 multifamily properties, 22 industrial/flex properties and land under development. Our principal objective is to invest in high quality properties in prime locations, then proactively manage, lease and direct ongoing capital improvement programs to improve their economic performance. The percentage of total real estate rental revenue by property group for 2008, 2007 and 2006, and the percent leased, calculated as the percentage of physical net rentable area leased, as of December 31, 2008, were as follows:

On a combined basis, our commercial portfolio was 94% leased at December 31, 2008, 97% leased at December 31, 2007 and 95% leased at December 31, 2006.

The commercial lease expirations for the next five years are as follows:

Total real estate rental revenue from continuing operations was $282.3 million for 2008, $252.7 million for 2007 and $205.9 million for 2006. During the three year period ended December 31, 2008, we acquired eight office buildings, ten medical office buildings, two retail centers, one multifamily building and five industrial/flex properties. We also placed into service from development one office building and two multifamily buildings. During that same time frame, we sold two office buildings and two industrial properties. These acquisitions and dispositions were the primary reason for the shifting of each group’s percentage of total real estate rental revenue reflected above.

No single tenant accounted for more than 3.5% of real estate rental revenue in 2008, 3.6% of revenue in 2007, and 3.7% of revenue in 2006. All federal government tenants in the aggregate accounted for approximately 2.1% of our 2008 total revenue. Federal government tenants include the Department of Defense, U.S. Patent and Trademark Office, Federal Bureau of Investigation, Office of Personnel Management, Secret Service, Federal Aviation Administration, NASA and the National Institutes of Health. Our larger non-federal government tenants include the World Bank, Sunrise Senior Living, Inc., INOVA Health Systems, URS Corporation, Lafarge North America, Inc., George Washington University, Westat, Inc., IQ Solutions and Sun Microsystems.

We expect to continue investing in additional income producing properties. We invest in properties which we believe will increase in income and value. Our properties typically compete for tenants with other properties throughout the respective areas in which they are located on the basis of location, quality and rental rates.

5

Table of Contents

Index to Financial Statements

In prior years, we have been engaged in significant ground-up development in order to further strengthen our portfolio with long-term growth prospects. In 2007 and 2008, we completed construction on three ground-up development projects. The first was Bennett Park, a 224-unit multifamily property located in Arlington, VA, with the majority of units delivered by the end of 2007. The second development project was The Clayborne Apartments, a 74-unit multifamily property located in Alexandria, VA. All of the units at Clayborne were delivered during the first quarter of 2008. Bennett Park and Clayborne were 78% and 64% leased, respectively, at December 31, 2008. The third development project was Dulles Station, a Class A office property located in Herndon, VA. Dulles Station is entitled for two office buildings totaling 540,000 square feet. The first 180,000 square foot office building was completed in the third quarter 2007, and was 86% leased at December 31, 2008. Construction of the 360,000 square foot second building remains in the planning phase.

We make capital improvements on an ongoing basis to our properties for the purpose of maintaining and increasing their value and income. Major improvements and/or renovations to the properties in 2008, 2007, and 2006 are discussed under the heading “Capital Improvements and Development Costs.”

Further description of the property groups is contained in Item 2, Properties and in Schedule III. Reference is also made to Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations.

On February 18, 2009, we had 307 employees including 229 persons engaged in property management functions and 78 persons engaged in corporate, financial, leasing, asset management and other functions.

Tax Treatment of Recent Disposition Activity

In June 2008, Sullyfield Center and The Earhart Building were sold for a gain of $15.3 million. The capital gain from the sales was paid out to shareholders. In September 2007, Maryland Trade Centers I and II were sold for a gain of $25.0 million. The proceeds from the sales were reinvested in replacement properties. We did not dispose of any of our properties in 2006. We distributed all of our 2008, 2007 and 2006 ordinary taxable income to our shareholders. No provision for income taxes was necessary in 2008, 2007 or 2006.

Availability of Reports

Copies of this Annual Report on Form 10-K, as well as our Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and any amendments to such reports are available, free of charge, on the Internet on our website www.writ.com. All required reports are made available on the website as soon as reasonably practicable after they are electronically filed with or furnished to the Securities and Exchange Commission. The reference to our website address does not constitute incorporation by reference of the information contained in the website and such information should not be considered part of this document.

Set forth below are the risks that we believe are material to our shareholders. We refer to the shares of beneficial interest in WRIT as our “common shares,” and the investors who own shares as our “shareholders.” This section includes or refers to certain forward-looking statements. You should refer to the explanation of the qualifications and limitations on such forward-looking statements beginning on page 50.

Recent disruptions in the financial markets could affect our ability to obtain financing or have other adverse effects on us or the market price of our common shares.

The United States and global equity and credit markets have recently experienced significant price volatility and liquidity disruptions which have caused the market prices of stocks to fluctuate substantially and the spreads on prospective debt financings to widen considerably. These circumstances have significantly negatively impacted liquidity in the financial markets, making terms for certain financings less attractive or unavailable. Continued uncertainty in the equity and credit markets will negatively impact our ability to access additional financing at reasonable terms or at all. In the event of a debt financing, our cost of borrowing in the future will likely be significantly higher than historical levels. In the case of a common equity financing, the disruptions in the financial markets could continue to have a material adverse effect on the market value of our common shares, potentially requiring us to issue more shares than we would otherwise have issued with a higher market value for our common shares. These financial market circumstances also will negatively affect our ability to make acquisitions, undertake new development projects and refinance our debt. These circumstances have also made it more difficult for us to sell properties and may adversely affect the price we receive for properties that we do sell, as prospective buyers are experiencing increased costs of financing and difficulties in obtaining financing.

6

Table of Contents

Index to Financial Statements

The current market conditions are also adversely affecting many of our tenants and their businesses, including their ability to pay rents when due and renew their leases at rates at least as favorable as their current rates. As well, our ability to attract prospective new tenants in the future could be adversely affected. There is a risk that government responses to the disruptions in the financial markets will not restore consumer confidence, stabilize the markets or increase liquidity and the availability of equity or credit financing.

Our performance and value are subject to risks associated with our real estate assets and with the real estate industry.

Our economic performance and the value of our real estate assets are subject to the risk that if our office, medical office, retail, multifamily and industrial properties do not generate revenues sufficient to meet our operating expenses, debt service and capital expenditures, our cash flow and ability to pay distributions to our shareholders will be adversely affected. The following factors, among others, may adversely affect the revenues generated by our commercial and multifamily properties:

We are dependent upon the economic climate of the Washington metropolitan region.

All of our properties are located in the Washington metropolitan region, which may expose us to a greater amount of market dependent risk than if we were geographically diverse. General economic conditions and local real estate conditions in our geographic region may be dependent upon one or more industries, thus a downturn in one of the industries may have a particularly strong effect. In particular, economic conditions in our market are directly affected by federal government spending in the region. In the event of reduced federal spending or negative economic changes in our region, we may experience a negative impact to our profitability and may be limited in our ability to make distributions to our shareholders.

We face risks associated with property acquisitions.

We intend to continue to acquire properties which would continue to increase our size and could alter our capital structure. Our acquisition activities and results may be exposed to the following risks:

7

Table of Contents

Index to Financial Statements

We may acquire properties subject to liabilities and without recourse, or with limited recourse with respect to unknown liabilities. As a result, if liability were asserted against us based upon the acquisition of a property, we may have to pay substantial sums to settle it, which could adversely affect our cash flow. Unknown liabilities with respect to properties acquired might include:

We face potential difficulties or delays renewing leases or re-leasing space.

From 2009 through 2013, leases on our commercial properties will expire on a total of approximately 67% of our leased square footage as of December 31, 2008, with leases on approximately 12% of our leased square footage expiring in 2009, 16% in 2010, 15% in 2011, 10% in 2012 and 14% in 2013. We derive substantially all of our income from rent received from tenants. Also, if our tenants decide not to renew their leases, we may not be able to re-let the space. If tenants decide to renew their leases, the terms of renewals, including the cost of required improvements or concessions, may be less favorable than current lease terms. As a result, our cash flow could decrease and our ability to make distributions to our shareholders could be adversely affected. Residential properties are leased under operating leases with terms of generally one year or less. For the years ended 2008, 2007 and 2006, the residential tenant retention rate was 67%, 67% and 68%, respectively.

We face potential adverse effects from major tenants’ bankruptcies or insolvencies.

The bankruptcy or insolvency of a major tenant may adversely affect the income produced by a property. During the fourth quarter of 2008, the bankruptcy of a large retail tenant caused a loss of approximately $1.0 million. In light of the current economic recession, it is possible that additional major tenants could file for bankruptcy protection or become insolvent in the future. We cannot evict a tenant solely because of its bankruptcy. On the other hand, a court might authorize the tenant to reject and terminate its lease. In such case, our claim against the bankrupt tenant for unpaid, future rent would be subject to a statutory cap that might be substantially less than the remaining rent actually owed under the lease, and, our claim for unpaid rent would likely not be paid in full. This shortfall could adversely affect our cash flow and results from operations.

If a tenant experiences a downturn in its business or other types of financial distress, it may be unable to make timely rental payments. Provision for losses on accounts receivable for the entire portfolio increased to $4.3 million in 2008, from $2.0 million in 2007 and $1.2 million in 2006. This unfavorable trend could continue or worsen in 2009 and forward.

We face risks associated with property development.

Developing properties present a number of risks for us, including risks that:

Properties developed or acquired for development may generate little or no cash flow from the date of acquisition through the date of completion of development. In addition, new development activities, regardless of whether or not they are ultimately successful, may require a substantial portion of management’s time and attention.

8

Table of Contents

Index to Financial Statements

These risks could result in substantial unanticipated delays or expenses and, under certain circumstances, could prevent completion of development activities once undertaken, any of which could have an adverse effect on our financial condition, results of operations, cash flow, the trading price of our common shares, and ability to satisfy our debt service obligations and to pay dividends to shareholders.

Our properties face significant competition.

We face significant competition from developers, owners and operators of office, medical office, retail, multifamily, industrial and other commercial real estate. Substantially all of our properties face competition from similar properties in the same market. Such competition may affect our ability to attract and retain tenants and may reduce the rents we are able to charge. These competing properties may have vacancy rates higher than our properties, which may result in their owners being willing to make space available at lower prices than the space in our properties.

We face risks associated with the use of debt to fund acquisitions and developments, including refinancing risk.

We rely on borrowings under our credit facilities and offerings of debt securities to finance acquisitions and development activities and for working capital. The commercial real estate debt markets are currently experiencing volatility due to a number of factors, including the tightening of underwriting standards by lenders and credit rating agencies and the reported significant inventory of unsold mortgage backed securities in the market. The volatility has resulted in investors decreasing the availability of debt financing as well as increasing the cost of debt financing. As a result, we may not be able to obtain debt financing in the future on favorable terms, or at all. If we were unable to borrow under our credit facilities or to refinance existing debt financing, our financial condition and results of operations would likely be adversely affected.

We are subject to the risks normally associated with debt, including the risk that our cash flow may be insufficient to meet required payments of principal and interest. We anticipate that only a small portion of the principal of our debt will be repaid prior to maturity. Therefore, we are likely to need to refinance at least a portion of our outstanding debt as it matures. There is a risk that we may not be able to refinance existing debt or that the terms of any refinancing will not be as favorable as the terms of the existing debt. If principal payments due at maturity cannot be refinanced, extended or repaid with proceeds from other sources, such as new equity capital, our cash flow may not be sufficient to repay all maturing debt in years when significant “balloon” payments come due.

Rising interest rates would increase our interest costs.

We may incur indebtedness that bears interest at variable rates. Accordingly, if interest rates increase, so will our interest costs, which could adversely affect our cash flow and our ability to service debt. As a protection against rising interest rates, we may enter into agreements such as interest rate swaps, caps, floors and other interest rate exchange contracts. These agreements, however, increase our risks that other parties to the agreements may not perform or that the agreements may be unenforceable.

Covenants in our debt agreements could adversely affect our financial condition.

Our credit facilities contain customary restrictions, requirements and other limitations on our ability to incur indebtedness. We must maintain a minimum tangible net worth and certain ratios, including a maximum of total liabilities to total gross asset value, a maximum of secured indebtedness to gross asset value, a minimum of annual EBITDA to fixed charges, a minimum of unencumbered asset value to unsecured indebtedness, a minimum of net operating income from unencumbered properties to unsecured interest expense and a maximum of permitted investments to gross asset value. Our ability to borrow under our credit facilities is subject to compliance with our financial and other covenants. The recent economic downturn and disruptions in the financial markets may adversely affect our ability to comply with these financial and other covenants.

Failure to comply with any of the covenants under our unsecured credit facilities or other debt instruments could result in a default under one or more of our debt instruments. This could cause our lenders to accelerate the timing of payments and would therefore have a material adverse effect on our business, operations, financial condition and liquidity.

Further issuances of equity securities may be dilutive to current shareholders.

The interests of our existing shareholders could be diluted if additional equity securities are issued to finance future developments and acquisitions instead of incurring additional debt. Our ability to execute our business strategy depends on our access to an appropriate blend of debt financing, including unsecured lines of credit and other forms of secured and unsecured debt, and equity financing.

9

Table of Contents

Index to Financial Statements

Compliance or failure to comply with the Americans with Disabilities Act and other laws could result in substantial costs.

The Americans with Disabilities Act generally requires that public buildings, including commercial and multifamily properties, be made accessible to disabled persons. Noncompliance could result in imposition of fines by the federal government or the award of damages to private litigants. If, pursuant to the Americans with Disabilities Act, we are required to make substantial alterations and capital expenditures in one or more of our properties, including the removal of access barriers, it could adversely affect our financial condition and results of operations, as well as the amount of cash available for distribution to our shareholders. We may also incur significant costs complying with other regulations. Our properties are subject to various federal, state and local regulatory requirements, such as state and local fair housing, rent control and fire and life safety requirements. If we fail to comply with these requirements, we may incur fines or private damage awards. We believe that our properties are currently in material compliance with all of these regulatory requirements. However, we do not know whether existing requirements will change or whether compliance with future requirements will require significant unanticipated expenditures that will adversely affect our cash flow and results from operations.

Some potential losses are not covered by insurance.

We carry insurance coverage on our properties of types and in amounts that we believe are in line with coverage customarily obtained by owners of similar properties. We believe all of our properties are adequately insured. The property insurance that we maintain for our properties has historically been on an “all risk” basis, which is in full force and effect until renewal in September 2009. There are other types of losses, such as from wars or catastrophic acts of nature, for which we cannot obtain insurance at all or at a reasonable cost. In the event of an uninsured loss or a loss in excess of our insurance limits, we could lose both the revenues generated from the affected property and the capital we have invested in the affected property. Depending on the specific circumstances of the affected property it is possible that we could be liable for any mortgage indebtedness or other obligations related to the property. Any such loss could adversely affect our business and financial condition and results of operations.

Also, we have to renew our policies in most cases on an annual basis and negotiate acceptable terms for coverage, exposing us to the volatility of the insurance markets, including the possibility of rate increases. Any material increase in insurance rates or decrease in available coverage in the future could adversely affect our results of operations and financial condition.

Potential liability for environmental contamination could result in substantial costs.

Under federal, state and local environmental laws, ordinances and regulations, we may be required to investigate and clean up the effects of releases of hazardous or toxic substances or petroleum products at our properties, regardless of our knowledge or responsibility, simply because of our current or past ownership or operation of the real estate. In addition, the U.S. Environmental Protection Agency, the U.S. Occupational Safety and Health Administration and other state and local governmental authorities are increasingly involved in indoor air quality standards, especially with respect to asbestos, mold, medical waste and lead-based paint. The clean up of any environmental contamination, including asbestos and mold, can be costly. If unidentified environmental problems arise, we may have to make substantial payments which could adversely affect our cash flow because:

These costs could be substantial and in extreme cases could exceed the value of the contaminated property. The presence of hazardous or toxic substances or petroleum products or the failure to properly remediate contamination may adversely affect our ability to borrow against, sell or rent an affected property. In addition, applicable environmental laws create liens on contaminated sites in favor of the government for damages and costs it incurs in connection with a contamination.

10

Table of Contents

Index to Financial Statements

We have a storage tank third party liability, corrective action and cleanup policy in place to cover potential hazardous releases from underground storage tanks on our properties. This insurance is in place to mitigate any potential remediation costs from the effect of releases of hazardous or toxic substances from these storage tanks. Additional coverage is in place under a pollution legal liability real estate policy. This would, dependent on circumstance and type of pollutants discovered, provide further coverage above and beyond the storage tank policy.

Environmental laws also govern the presence, maintenance and removal of asbestos. Such laws require that owners or operators of buildings containing asbestos:

Such laws may impose fines and penalties on building owners or operators who fail to comply with these requirements and may allow third parties to seek recovery from owners or operators for personal injury associated with exposure to asbestos fibers.

It is our policy to retain independent environmental consultants to conduct Phase I environmental site assessments and asbestos surveys with respect to our acquisition of properties. These assessments generally include a visual inspection of the properties and the surrounding areas, an examination of current and historical uses of the properties and the surrounding areas and a review of relevant state, federal and historical documents, but do not always involve invasive techniques such as soil and ground water sampling. Where appropriate, on a property-by-property basis, our practice is to have these consultants conduct additional testing, including sampling for asbestos, for mold, for lead in drinking water, for soil contamination where underground storage tanks are or were located or where other past site usages create a potential environmental problem, and for contamination in groundwater. Even though these environmental assessments are conducted, there is still the risk that:

Failure to qualify as a REIT would cause us to be taxed as a corporation, which would substantially reduce funds available for payment of dividends.

If we fail to qualify as a REIT for federal income tax purposes, we would be taxed as a corporation. We believe that we are organized and qualified as a REIT and intend to operate in a manner that will allow us to continue to qualify as a REIT.

If we fail to qualify as a REIT we could face serious tax consequences that could substantially reduce the funds available for payment of dividends for each of the years involved because:

In addition, if we fail to qualify as a REIT, we would no longer be required to pay dividends. As a result of these factors, our failure to qualify as a REIT could impair our ability to expand our business and raise capital, and could adversely affect the value of our shares.

11

Table of Contents

Index to Financial Statements

Recently enacted changes in securities laws are likely to increase our costs.

The Sarbanes-Oxley Act of 2002, as well as rules subsequently implemented by the Securities and Exchange Commission, has required changes in some of our corporate governance and accounting practices. In addition, the New York Stock Exchange has promulgated a number of regulations. We expect these laws, rules and regulations to increase our legal and financial compliance costs and to continue to make some activities more difficult, time consuming and costly. We also expect these rules and regulations to continue to make it more difficult and more expensive for us to obtain director and officer liability insurance, and we incur significantly higher costs to obtain coverage. These laws, rules and regulations could also make it more difficult for us to attract and retain qualified members of our board of trustees, particularly to serve on our audit committee, and qualified executive officers.

The market value of our securities can be adversely affected by many factors.

As with any public company, a number of factors may adversely influence the public market price of our common shares, most of which are beyond our control. These factors include:

Provisions of the Maryland General Corporation Law, or the MGCL, may limit a change in control.

There are several provisions of the Maryland General Corporation Law, or the MGCL, that may limit the ability of a third party to undertake a change in control, including:

These provisions may delay, defer, or prevent a transaction or a change in control that may involve a premium price for holders of our shares or otherwise be in their best interests.

None.

12

Table of Contents

Index to Financial Statements

The schedule on the following pages lists our real estate investment portfolio as of December 31, 2008, which consisted of 93 properties and land under development.

As of December 31, 2008, the percent leased is the percentage of net rentable area for which fully executed leases exist and may include signed leases for space not yet occupied by the tenant.

Cost information is included in Schedule III to our financial statements included in this Annual Report on Form 10-K.

Schedule of Properties

13

Table of Contents

Index to Financial Statements

SCHEDULE OF PROPERTIES (continued)

14

Table of Contents

Index to Financial Statements

SCHEDULE OF PROPERTIES (continued)

None.

No matters were submitted to a vote of security holders during the fourth quarter of 2008.

15

Table of Contents

Index to Financial Statements

PART II

Our shares trade on the New York Stock Exchange. Currently, there are approximately 6,789 shareholders of record.

The high and low sales price for our shares for 2008 and 2007, by quarter, and the amount of dividends we paid per share are as follows:

We have historically paid dividends on a quarterly basis. Dividends are primarily paid from our cash flow from operating activities.

During the period covered by this report, we did not sell equity securities without registration under the Securities Act.

Neither we nor any affiliated purchaser (as that term is defined in Securities Exchange Act Rule 10b-18(a) (3)) made any repurchases of our shares during the fourth quarter of the fiscal year covered by this report.

16

Table of Contents

Index to Financial Statements

The following table sets forth our selected financial data on a historical basis, which has been revised for properties disposed of or classified as held for sale in accordance with SFAS No. 144. Refer to Note 3 of the consolidated financial statements. The following data should be read in conjunction with our financial statements and notes thereto and Management’s Discussion and Analysis of Financial Condition and Results of Operations included elsewhere in this Form 10-K.

17

Table of Contents

Index to Financial Statements

Overview

Our revenues are derived primarily from the ownership and operation of income-producing properties in the greater Washington metro region. As of December 31, 2008, we owned a diversified portfolio of 93 properties, consisting of 28 office properties, 22 industrial/flex properties, 17 medical office properties, 14 retail centers, and 12 multifamily properties, encompassing in the aggregate 13.0 million net rentable square feet, and land for development. We have a fundamental strategy of regional focus, diversification by property type and conservative capital management.

When evaluating our financial condition and operating performance, we focus on the following financial and non-financial indicators, discussed in further detail herein:

During 2008, we continued our fundamental strategy of investing in diversified property types in the greater Washington metro region. The area’s economy softened as the national economy moved into recession. The unemployment rate for the Washington metro area is 4.1%, compared to 6.5% nationally, as of October 2008. Job growth increased 1.2%, compared to a 1.4% decline nationally. Government, professional and business services, and education and health sectors, led job growth in the metro area in 2008. The Washington metro area’s economic growth is forecasted to moderate in 2009, adding 24,000 new payroll jobs, according to Delta Associates and economist Dr. Steven Fuller of George Mason University.

Our results of operations in 2008 were primarily impacted by acquisitions and dispositions and the performance of our core portfolio. We completed total acquisitions and dispositions totaling $576.7 million and $99.1 million, respectively, during the prior two years. The performance of our core portfolio, consisting of properties owned for the entirety of 2008 and the same time period in 2007, declined compared to 2007, primarily due to lower occupancy and higher bad debt expense.

18

Table of Contents

Index to Financial Statements

The performance of our five operating segments generally reflected market conditions in our region:

During 2008, we completed the development of Dulles Station Phase I, Bennett Park and Clayborne Apartments. Dulles Station Phase One is a Class A office property located in Herndon, VA. Bennett Park is a Class A high-rise and mid-rise apartment community with retail space located in Arlington, VA. The Clayborne Apartments is a Class A apartment building with retail space located in Alexandria, VA.

We summarize below our significant transactions during the two years ended December 31, 2008:

2008

19

Table of Contents

Index to Financial Statements

2007

20

Table of Contents

Index to Financial Statements

Critical Accounting Policies and Estimates

The discussion and analysis of our financial condition and results of operations are based upon our consolidated financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States. The preparation of these financial statements requires us to make estimates and judgments that affect the reported amounts of assets, liabilities, revenues and expenses. On an on-going basis, we evaluate these estimates, including those related to estimated useful lives of real estate assets, estimated fair value of acquired leases, cost reimbursement income, bad debts, contingencies and litigation. We base the estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. There can be no assurance that actual results will not differ from those estimates.

We believe the following critical accounting policies reflect the significant judgments and estimates used in the preparation of our consolidated financial statements. Our significant accounting policies are also described in Note 2 to the consolidated financial statements in Item 8 of this Form 10-K.

Revenue Recognition

Our multifamily properties are leased under operating leases with terms of generally one year or less, and our commercial properties (our office, medical office, retail and industrial segments) are leased under operating leases with average terms of three to seven years. We recognize real estate rental revenue and rental abatements from our residential and commercial leases when earned on a straight-line basis in accordance with SFAS No. 13, Accounting for Leases. Recognition of real estate rental revenue commences when control of the facility has been given to the tenant. We record a provision for losses on accounts receivable equal to the estimated uncollectible amounts. This estimate is based on our historical experience and a review of the current status of our receivables. Percentage rents, which represent additional rents based on gross tenant sales, are recognized when tenant sales exceed specified thresholds.

In accordance with SFAS No. 66, Accounting for Sales of Real Estate, sales are recognized at closing only when sufficient down payments have been obtained, possession and other attributes of ownership have been transferred to the buyer and we have no significant continuing involvement.

We recognize cost reimbursement income from pass-through expenses on an accrual basis over the periods in which the expenses were incurred. Pass-through expenses are comprised of real estate taxes, operating expenses and common area maintenance costs which are reimbursed by tenants in accordance with specific allowable costs per tenant lease agreements.

Accounts Receivable and Allowance for Doubtful Accounts

Accounts receivable primarily represents amounts accrued and unpaid from tenants in accordance with the terms of the respective leases, subject to our revenue recognition policy. Receivables are reviewed monthly and reserves are established when, in the opinion of management, collection of the receivable is doubtful. Reserves are established for tenants whose rent payment history or financial condition casts doubt upon the tenant’s ability to perform under its lease obligation. When the collection of a receivable is deemed doubtful in the same quarter that the receivable was established, then the allowance for that receivable is recognized as an offset to real estate revenues. When a receivable that was initially established in a prior quarter is deemed doubtful, then the allowance is recognized as an operating expense. In addition to rents due currently, accounts receivable include amounts representing minimal rental income accrued on a straight-line basis to be paid by tenants over the remaining term of their respective leases.

Included in our accounts receivable balance are notes receivable totaling $7.4 million and $0.4 million as of December 31, 2008 and 2007, respectively. $7.3 million of the 2008 balance represents the fair value of a note receivable acquired with 2445 M Street during the fourth quarter of 2008. The note receivable is from a prior tenant at that property.

Real Estate and Depreciation

We depreciate buildings on a straight-line basis over estimated useful lives ranging from 28 to 50 years. We capitalize all capital improvement expenditures associated with replacements, improvements or major repairs to real property that extend its useful life and depreciate them using the straight-line method over their estimated useful lives ranging from

21

Table of Contents

Index to Financial Statements

three to 30 years. We also capitalize costs incurred in connection with our development projects, including capitalizing interest and other internal costs during periods in which qualifying expenditures have been made and activities necessary to get the development projects ready for their intended use are in progress. In addition, we capitalize tenant leasehold improvements when certain criteria are met, including when we supervise construction and will own the improvements. We depreciate all tenant improvements over the shorter of the useful life of the improvements or the term of the related tenant lease. Real estate depreciation expense from continuing operations for the years ended December 31, 2008, 2007 and 2006 was $69.2 million, $55.7 million and $44.1 million, respectively. Maintenance and repair costs that do not extend an asset’s life are charged to expense as incurred.

We capitalize interest costs incurred on borrowing obligations while qualifying assets are being readied for their intended use in accordance with SFAS No. 34, Capitalization of Interest Cost. Total interest expense capitalized to real estate assets related to development and major renovation activities was $2.1 million, $6.1 million and $3.8 million, for the years ended December 31, 2008, 2007 and 2006, respectively. Interest capitalized is amortized over the useful life of the related underlying assets upon those assets being placed into service.

We recognize impairment losses on long-lived assets used in operations and held for sale, development assets or land under development, if indicators of impairment are present and the net undiscounted cash flows estimated to be generated by those assets are less than the assets’ carrying amount and estimated undiscounted cash flows associated with future development expenditures. If such carrying amount is in excess of the estimated cash flows from the operation and disposal of the property, we would recognize an impairment loss equivalent to an amount required to adjust the carrying amount to the estimated fair value. During 2008, we expensed $0.6 million, included in general and administrative expenses, related to development projects no longer considered probable. There were no property impairments recognized during the periods ended December 31, 2007 and 2006.

We allocate the purchase price of acquired properties to the related physical assets and in-place leases based on their fair values, in accordance with SFAS No. 141, Business Combinations. The total acquisition cost comprises the acquisition-date fair value of all assets transferred, equity issued, and liabilities assumed. The fair values of acquired buildings are determined on an “as-if-vacant” basis considering a variety of factors, including the physical condition and quality of the buildings, estimated rental and absorption rates, estimated future cash flows and valuation assumptions consistent with current market conditions. The “as-if-vacant” fair value is allocated to land, building and tenant improvements based on property tax assessments and other relevant information obtained in connection with the acquisition of the property. No goodwill was recorded on our acquisitions for the years ended December 31, 2008, 2007 and 2006.

The fair value of in-place leases consists of the following components – (a) the estimated cost to us to replace the leases, including foregone rents during the period of finding a new tenant and foregone recovery of tenant pass-throughs (referred to as “absorption cost”), (b) the estimated cost of tenant improvements, and other direct costs associated with obtaining a new tenant (referred to as “tenant origination cost”); (c) estimated leasing commissions associated with obtaining a new tenant (referred to as “leasing commissions”); (d) the above/at/below market cash flow of the leases, determined by comparing the projected cash flows of the leases in place to projected cash flows of comparable market-rate leases (referred to as “net lease intangible”); and (e) the value, if any, of customer relationships, determined based on our evaluation of the specific characteristics of each tenant’s lease and our overall relationship with the tenant (referred to as “customer relationship value”). We have attributed no value to customer relationship value as of December 31, 2008 or 2007.

The amounts used to calculate net lease intangible are discounted using an interest rate which reflects the risks associated with the leases acquired. Tenant origination costs are included in income producing property on our balance sheet and are amortized as depreciation expense on a straight-line basis over the remaining life of the underlying leases. Leasing commissions and absorption costs are classified as other assets and are amortized as amortization expense on a straight-line basis over the remaining life of the underlying leases. Net lease intangible assets are classified as other assets and are amortized on a straight-line basis as a decrease to real estate rental revenue over the remaining term of the underlying leases. Net lease intangible liabilities are classified as other liabilities and are amortized on a straight-line basis as an increase to real estate rental revenue over the remaining term of the underlying leases. Should a tenant terminate its lease, the unamortized portion of the tenant origination cost, leasing commissions, absorption costs and net lease intangible associated with that lease are written off.

Federal Income Taxes

We believe that we qualify as a REIT under Sections 856-860 of the Internal Revenue Code and intend to continue to qualify as such. To maintain our status as a REIT, we are required to distribute 90% of our ordinary taxable income to our shareholders. When selling properties, we have the option of (a) reinvesting the sale price of properties sold,

22

Table of Contents

Index to Financial Statements

allowing for a deferral of income taxes on the sale, (b) paying out capital gains to the shareholders with no tax to us or (c) treating the capital gains as having been distributed to our shareholders, paying the tax on the gain deemed distributed and allocating the tax paid as a credit to our shareholders. In June 2008, two industrial properties, Sullyfield Center and The Earhart Building, were sold for a gain of $15.3 million. The proceeds from the sales were treated as a distribution to shareholders. In September 2007, Maryland Trade Centers I and II were sold for a gain of $25.0 million. The proceeds from the sale were reinvested in replacement properties. We did not dispose of any of our properties in 2006, and we distributed all of our 2008, 2007 and 2006 ordinary taxable income to our shareholders. No provision for income taxes was necessary in 2008, 2007 or 2006.

Results of Operations

The discussion that follows is based on our consolidated results of operations for the years ended December 31, 2008, 2007 and 2006. The ability to compare one period to another may be significantly affected by acquisitions completed and dispositions made during those years.

For purposes of evaluating comparative operating performance, we categorize our properties as “core”, “non-core” or discontinued operations. A “core” property is one that was owned for the entirety of the periods being evaluated and is included in continuing operations. A “non-core” property is one that was acquired or placed into service during either of the periods being evaluated and is included in continuing operations. Results for properties sold or held for sale during any of the periods evaluated are classified as discontinued operations. A total of four properties were acquired during 2008, eight properties and land for development were acquired during 2007 and fourteen properties were acquired during 2006. Two development properties were placed into service in 2008, and one development property was placed into service during 2007. Two properties were sold and one property was classified as held for sale in 2008, and two properties were sold in 2007. These held for sale and sold properties are classified as discontinued operations for the 2008, 2007 and 2006 periods. There were no properties sold or classified as held for sale in 2006.

To provide more insight into our operating results, our discussion is divided into two main sections: (a) the consolidated results of operations section, in which we provide an overview analysis of results on a consolidated basis, and (b) the net operating income (“NOI”) section, in which we provide a detailed analysis of core versus non-core NOI results by segment. NOI is a non-GAAP measure calculated as real estate rental revenue less real estate operating expenses.

Consolidated Results of Operations

Real Estate Rental Revenue

Real estate rental revenue for properties classified as continuing operations is summarized as follows (all data in thousands except percentage amounts):

Real estate rental revenue is comprised of (a) minimum base rent, which includes rental revenues recognized on a straight-line basis, (b) revenue from the recovery of operating expenses from our tenants, (c) provisions for doubtful accounts, which includes provisions for straight-line receivables, (d) revenue from the collection of lease termination fees and (e) parking and other tenant charges such as percentage rents.

Minimum Base Rent: Minimum base rent increased by $24.5 million in 2008 as compared to 2007 due primarily to properties acquired or placed into service in 2008 and 2007 ($22.5 million), combined with a $2.0 million increase in minimum base rent from core properties due to higher rental rates in all segments, partially offset by higher vacancy in the commercial segments.

23

Table of Contents

Index to Financial Statements

Minimum base rent increased by $38.4 million in 2007 as compared to 2006 due primarily to properties acquired or placed into service in 2007 and 2006 ($31.6 million), combined with a $7.4 million increase in minimum base rent from core properties due to increased occupancy in the office and industrial segments and rental rate increases in all segments.

Recoveries from Tenants: Recoveries from tenants increased by $5.9 million in 2008 as compared to 2007 due primarily to properties acquired or placed into service in 2008 and 2007 ($4.0 million), combined with a $1.9 million increase in recoveries from tenants from core properties primarily due to higher real estate tax reimbursements ($1.6 million) and common area maintenance reimbursements ($0.2 million).

Recoveries from tenants increased by $7.7 million in 2007 as compared to 2006 due primarily to properties acquired or placed into service in 2007 and 2006 ($4.0 million), combined with a $3.7 million increase in recovery income from core properties due to higher operating expenses and utilities ($0.9 million), common area maintenance ($0.9 million) and real estate taxes ($1.8 million).

Provisions for Doubtful Accounts: Provisions for doubtful accounts increased by $2.6 million in 2008 as compared to 2007 due to higher provisions in the retail ($1.0 million), industrial ($1.0 million) and office ($0.6 million) segments. Provisions for bad debt in the multifamily and medical office segments were flat. The higher overall provision is reflective of the economic recession that began in 2008. In addition to the provision for doubtful accounts included in real estate rental revenue, net recoveries of previously written-off receivables of $0.3 million were recorded in property operating expenses.

Provisions for doubtful accounts increased by $0.8 million in 2007 as compared to 2006.

Lease Termination Fees: Lease termination fees increased by $0.8 million in 2008 as compared to 2007 due primarily to higher fees in the office ($0.8 million) and industrial ($0.2 million) segments, partially offset by lower fees in the retail segment ($0.2 million).

Lease termination fees increased slightly by $0.2 million in 2007 as compared to 2006.

Parking and Other Tenant Charges: Parking and other tenant charges increased by $1.1 million in 2008 as compared to 2007 due primarily to higher parking revenue ($0.8 million) and miscellaneous fees ($0.3 million).

Parking and other tenant charges increased by $1.3 million in 2007 as compared to 2006 due to higher parking revenue and antenna rent.

A summary of economic occupancy for properties classified as continuing operations by segment follows:

Consolidated Economic Occupancy

Economic occupancy represents actual real estate rental revenue recognized for the period indicated as a percentage of gross potential real estate rental revenue for that period. Percentage rents and expense reimbursements are not considered in computing economic occupancy percentages.

Our overall economic occupancy decreased to 92.3% in 2008 from 94.5% in 2007, driven primarily by the lease-up during 2008 of our development properties in the office and multifamily segments. Our development properties Bennett Park, Clayborne Apartments and Dulles Station, Phase I were placed into service at the end of 2007 and during 2008, and were 78%, 64% and 86% leased at year-end, respectively.

Overall economic occupancy increased to 94.5% in 2007 from 93.8% in 2006 due primarily to occupancy gains in the office and industrial segments.

24

Table of Contents

Index to Financial Statements

A detailed discussion of occupancy by sector can be found in the Net Operating Income section.

Real Estate Expenses

Real estate expenses are summarized as follows (all data in thousands except percentage amounts):