CoStar Group to Report Financial Results for Fourth Quarter and Full-Year 2008 On February 18, 2009

Earnings Report to be Issued After Market Close On Wednesday, February 18; Conference Call to Discuss 2008 Financial Results and Company's Outlook for 2009 Scheduled for 11:00 AM EST On Thursday, February 19

CoStar Group, Inc. (Nasdaq:CSGP), the number one provider of information/marketing services to the commercial real estate industry, will announce financial results for the fourth quarter and full-year of 2008 following the market close on Wednesday, February 18, 2009. Management will conduct a conference call to discuss the results and the company's outlook for 2009 at 11:00 AM EST on Thursday, February 19.

To participate in the conference call, please dial (80... (from the United States and Canada) or (612) 288-0340 (from all other countries) and refer to conference 984704. Investors may also listen to an audio webcast of this conference call by accessing the link in the Investors section of CoStar's web site at www.CoStar.com.

An audio recording of the conference will be available for replay approximately one hour after the call's completion and remain available through midnight on March 5, 2009. To access the recorded call, please dial (800) 4... (from the U.S. and Canada) or (320) 3... (from all other countries) using access code 984704. The webcast replay will also be available in the Investors section of CoStar Group's web site for a period of time following the call.

About CoStar Group, Inc.

CoStar Group, Inc. (Nasdaq:CSGP) is the number one provider of information/marketing services to commercial real estate professionals in the United States as well as the United Kingdom. CoStar's suite of services offers customers access via the Internet to the most comprehensive database of commercial real estate information throughout the U.S. as well as in the United Kingdom and France. Headquartered in Bethesda, MD, CoStar has approximately 1,300 people working for the company worldwide, including the largest professional research organization in the industry. For more information, visit http://www.costar.com.

This news release includes "forward-looking statements" including, without limitation, statements regarding CoStar's expectations, beliefs, intentions or strategies regarding the future. These statements are subject to many risks and uncertainties that could cause actual results to differ materially from these statements. More information about potential factors that could cause actual results to differ materially from those discussed in the forward-looking statements include, but are not limited to, those stated in CoStar's filings from time to time with the Securities and Exchange Commission, including CoStar's Form 10-K for the year ended December 31, 2007, and CoStar's Form 10-Q for the quarter ended September 30, 2008, under the heading "Risk Factors." All forward-looking statements are based on information available to CoStar on the date hereof, and CoStar assumes no obligation to update such statements.

CONTACT: CoStar Group, Inc.
Analysts/Investors:
Brian J. Radecki, Chief Financial Officer
(301) 664-9132
bradecki@costar.com
Media:
Timothy J. Trainor, Communications Director
(301) 280-7695
ttrainor@costar.com
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