COSTAR GROUP, INC. — Director's Dealing 2012

May 30, 2012

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: COSTAR GROUP INC (CSGP)
CIK: 0001057352
Period of Report: 2012-05-29

Reporting Person: BONDERMAN DAVID (Director)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2012-05-29	Common Stock, par value $0.01 per share	M	5000	$22.87	Acquired	281086	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2012-05-29	Option to Acquire Common Stock	$22.87	M	5000	Disposed	2012-09-08	Common Stock (5000)	Direct

Footnotes

F1: Represents all shares of Common Stock owned, consisting of 277,114 shares of Common Stock and 3,972 shares of Common Stock subject to unvested Restricted Stock Grants.

F2: The option vested in four equal installments on September 9, 2003, September 9, 2004, September 9, 2005 and September 9, 2006.