COSTAR GROUP, INC. — Director's Dealing 2011

Mar 8, 2011

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: COSTAR GROUP INC (CSGP)
CIK: 0001057352
Period of Report: 2011-03-04

Reporting Person: Marples Paul (Managing Director, FOCUS)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2011-03-04	Common Stock, par value $0.01 per share	S	1500	$57.25	Disposed	15902	Direct
2011-03-04	Common Stock, par value $0.01 per share	A	2500	—	Acquired	18402	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2011-03-04	Option to Acquire Common Stock	$57.16	A	5900	Acquired	2021-03-03	Common Stock (5900)	Direct

Footnotes

F1: Average based on sales prices ranging from $57.19 to $57.29.

F2: Represents all shares of Common Stock owned, consisting of shares of 11,335 Common Stock and 4,567 shares of Common Stock subject to unvested Restricted Stock Grants.

F3: Represents all shares of Common Stock owned, consisting of 11,335 shares of Common Stock and 7,067 shares of Common Stock subject to unvested Restricted Stock Grants.

F4: The option vests in three equal installments on March 4, 2012, March 4, 2013, and March 4, 2014.