On October 21, 2009, CoStar Group, Inc. announced its financial results for the quarter ended September 30, 2009. The full text of the press release (the "Press Release") issued in connection with the announcement is attached as Exhibit 99.1 to this Current Report on Form 8-K.

The information contained in the Press Release shall be considered "furnished" pursuant to this Current Report on Form 8-K and shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, nor shall it be deemed incorporated by reference into any of the Registrant's reports or filings with the Securities and Exchange Commission, whether made before or after the date hereof, except as expressly set forth by specific reference in such a filing.

Exhibit No.                Description

Exhibit 99.1                CoStar Group, Inc. Press Release Dated October 21,
2009

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                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Name: Brian J. Radecki Title: Chief Financial Officer