SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549


SCHEDULE 13G


Under the Securities Exchange Act of 1934
(Amendment No. 3)



CoStar Group, Inc.
(Name of Issuer)

Common Stock (Par Value $.01)
(Title of Class of Securities)

22160N109
(CUSIP Number)

12/31/04 
(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule 
is filed:

[X] Rule 13d-1(b)
[  ] Rule 13d-1(c)
[  ] Rule 13d-1(d)

Check the following box if a fee is being paid with this statement [ ].  A fee 
is not required only if the filing person: (1) has a previous statement on file 
reporting  beneficial ownership of more than five percent of the class of 
securities described in Item 1; and (2) has filed no amendment subsequent 
there to reporting beneficial  ownership of five percent or less of such class. 
(See Rule 13d-7).

The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter 
the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be 
deemed  to be "filed" for the purpose of Section 18 of the Securities Exchange 
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of 
the Act but shall be subject to all other provisions of the Act (however, 
see the Notes).








1.	NAME OF REPORTING PERSONS.  I.R.S. IDENTIFICATION NOS. 
	OF ABOVE PERSONS (ENTITIES ONLY)

	Brown Advisory Holdings Incorporated ("BAHI")  


2. 	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
	(a) [ ]
	(b) [ ] 

3. 	SEC USE ONLY 

4. 	CITIZENSHIP OR PLACE OF ORGANIZATION

	BAHI is a Maryland Corporation.



			5 SOLE VOTING POWER		                   654883 shares
NUMBER OF 		
SHARES			          			   
BENEFICIALLY		6 SHARED VOTING POWER	          	           	           0 shares	
OWNED BY			           
EACH			
REPORTING		7 SOLE DISPOSITIVE POWER		                    810309 shares	
PERSON WITH			   	
			
			8 SHARED DISPOSITIVE POWER	                            8084 shares
		                  
					

9. 	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
              
	819228 shares


10. 	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN 
	SHARES [   ]


11. 	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	4.5%


12. 	TYPE OF REPORTING PERSON

                  BAHI - HC
		





Item 1(a). 	Name of Issuer:    

Costar Group, Inc.

Item 1(b). 	Address of Issuer's Principal Executive Offices:

2 Bethesda Metro Center, 10th Floor, Bethesda, MD  20814-5388

Item 2(a). 	Name of Person Filing:

BAHI


Item 2(b).	Address of Principal Business Office: 

901 South Bond Street, Suite 400
Baltimore, Maryland 21231

Item 2(c). 	Citizenship: 

BAHI is a Maryland Corporation.

Item 2(d). 	Title of Class of Securities: 

Common Stock (Par Value $.01) of CoStar Group, Inc.

Item 2(e).	CUSIP Number: 22160N109

Item 3. 	If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b), 
	check whether the person filing is a: 
	
(g) [x] 	A parent holding company or control person in accordance with section
	240.13d-1(b)(1)(ii)(G) 

Item 4. 	Ownership:

(a) 	Amount of Beneficially Owned:				 819228 shares

(b) 	Percent of Class:	         					4.5%

(c) 	Number of shares as to which such person has:

	(i)              Sole power to vote or to direct the vote:	   	  654883 shares

	(ii)	Shared power to vote or to direct the vote: 		          0 shares

	(iii) 	Sole power to dispose or to direct the disposition of:	 810309 shares

	(iv)	Shared power to dispose or to direct the disposition of:      8084 shares




Item 5. 	Ownership of Five Percent or Less of a Class. 

	If this statement is being filed to report the fact that as of the date hereof
	the reporting person has ceased to be the beneficial owner of more than
	five percent of the class of securities, check the following [X].

Item 6. 	Ownership of More than Five Percent on Behalf of Another Person.
	
	Not applicable

Item 7. 	Identification and Classification of the Subsidiary Which Acquired the 
	Security Being Reported on by the Parent Holding Company or Control Person.

	This Schedule is being filed pursuant to Rule 13d-1(b)(1)(ii)(G). 
	Refer to Exhibit A.
		
Item 8. 	Identification and Classification of Members of the Group.

	Not applicable

Item 9. 	Notice of Dissolution of Group.

	Not applicable

Item 10. 	Certification. 

	By signing below I certify that to the best of my knowledge and belief, the
	securities referred to above were acquired in the ordinary course of business 
	and were not acquired for the purpose of and do not have the effect of 
	changing or influencing the control of the issuer of such securities and were
	not acquired in connection with or as a participant in any transaction having
	such purpose or effect.   

	Signature:

	After reasonable inquiry and to the best of my knowledge and belief, I 
	certify that the information set forth in this statement is true, complete 
	and correct.


	Date:	As of December 31, 2004

	Signature:	Brown Advisory Holdings Incorporated

		By: /S/ Christopher P. Laia	
		
	Title:	Secretary


	Joint Filing Agreement
	----------------------------

	Each party signing below agrees that this statement is submitted as a joint
	filing on behalf of the undersigned.

	Date:	As of December 31, 2004

	Signature:	Brown Investment Advisory and Trust Company

	                  By: /S/ Patrick Ventura	
		
	Title:	Principal


	Date:	As of December 31, 2004

	Signature:	Brown Investment Advisory Incorporated

		By: /S/ Patrick Ventura	
		
	Title:	Principal














Exhibit A

Pursuant to the instructions in Item 7 of this Schedule 13G, the identity and
the Item 3 classification of the relevant subsidiaries are: BIATC, a Bank as
defined in Section 3(a)(6) of the Act; and Brown Investment Advisory
Incorporated, an Investment Advisor registered under section 203 of the
Investment Advisers Act of 1940 and a wholly-owned subsidiary of BIATC.