Effective January 1, 2009, Corporate Office Properties Trust (the "Registrant") retrospectively adopted Statement of Financial Accounting Standards No. 160, "Noncontrolling Interests in Consolidated Financial Statements," FASB Staff Position No. APB 14-1, "Accounting for Convertible Debt Instruments That May Be Settled in Cash upon Conversion (Including Partial Cash Settlement)" and EITF 03-6-1, "Determining Whether Instruments Granted in Share-Based Payment Transactions are Participating Securities." This resulted in the recording of certain adjustments to amounts previously reported, including changes that affected the Registrant's previously reported net income attributable to common shareholders and earnings per common share. These adjustments are described in further detail in Note 2 to the Consolidated Financial Statements included in Exhibit 99.4. The Registrant is filing this Current Report on Form 8-K to update Items 6, 7, 7A and 8 of its 2008 Annual Report on Form 10-K and Exhibit 12.1 to its 2008 Annual Report on Form 10-K to reflect the retrospective effects of these adjustments. The updates to the Registrant's 2008 Annual Report on Form 10-K included in the attached exhibits do not attempt to modify or update any other disclosures set forth in the the Registrant's 2008 Annual Report on Form 10-K filed on February 27, 2009, except as required to reflect the adjustments described above, and do not update or discuss any other developments affecting the Registrant subsequent to February 27, 2009.

(d) Exhibits

Exhibit Number                               Exhibit Title

23.1              Consent of Independent Registered Public Accounting Firm
                  (PricewaterhouseCoopers LLP).
99.1              Item 6. Selected Financial Data as of and for the years ended
                  December 31, 2008, 2007, 2006, 2005 and 2004.
99.2              Item 7. Management's Discussion and Analysis of Financial Condition
                  and Results of Operations.
99.3              Item 7A. Quantitative and Qualitative Disclosures about Market
                  Risk.
99.4              Consolidated Financial Statements and Schedule III included in Item
                  8.
99.5              Exhibit 12.1. Ratio of Earnings to Combined Fixed Charges and
                  Preferred Share Dividends.