NxStage Medical: Ownership Profile

Shareholder Breakdown
	Holders	Values ($)	% O/S	Shares
Institution	134	930,870,003.00	94.00	51,887,960
Mutual Fund	274	461,198,727.00	46.57	25,707,844

Institutional Shareholder Rotation
	Holders	Values Change ($)	% O/S	Shares Change
Buyers	69	112,621,688.00	48.33	6,277,686
Sellers	41	-94,502,375.00	39.48	-5,267,691
Net	--	18,119,313.00	8.85	1,009,995

Institutional Shareholder Concentration
	Values ($)	% O/S	Shares
Top 10 Inst.	495,131,961	50.00	27,599,329
Top 20 Inst.	670,226,954.00	67.68	37,359,362
Top 50 Inst.	879,750,025.00	88.84	49,038,463
Total Inst.	930,870,003.00	94.00	51,887,960

Institutional Shareholder Style
	Holders	Values ($)	% O/S	Shares
GARP	73	302,459,879	32.49	16,859,525
Value	24	84,581,862	9.09	4,714,708
Aggressive Growth	19	331,716,106	35.64	18,490,307
Growth	8	101,930,667	10.95	5,681,754
Index	8	109,392,972	11.75	6,097,713
Yield	2	788,517	0.08	43,953

Top Holders: Institutional Investor
	Shares Held	% O/S	Shares Change	Filing Date
Wells Capital Management, Inc.	5,008,822	9.07	1,183,792	12/31/2011
Gilder, Gagnon, Howe & Co. LLC	3,428,131	6.21	-390,821	12/31/2011
William Blair & Co. LLC (Investment Management)	3,229,468	5.85	-56,676	12/31/2011
OrbiMed Advisors, Inc.	2,730,143	4.95	0	12/31/2011
Next Century Growth Investors LLC	2,695,819	4.88	19,501	12/31/2011
AllianceBernstein LP	2,585,234	4.68	356,461	12/31/2011
BlackRock Fund Advisors	2,326,310	4.21	31,140	12/31/2011
The Vanguard Group, Inc.	2,151,126	3.90	132,398	12/31/2011
Fidelity Management & Research Co.	1,928,661	3.49	-130,878	12/31/2011
MFS Investment Management, Inc.	1,515,615	2.75	-76,554	12/31/2011
Cortina Asset Management LLC	1,383,450	2.51	-27,276	12/31/2011
Credit Suisse (United States)	1,243,175	2.25	-862,923	01/09/2012
Oracle Investment Management, Inc.	1,170,300	2.12	-2,000	12/31/2011
Deerfield Management Co. LP	1,099,462	1.99	-1,007,882	12/31/2011
State Street Global Advisors	865,441	1.57	32,942	12/31/2011
Chartwell Investment Partners LP	855,634	1.55	-26,455	12/31/2011
Sentinel Asset Management, Inc.	823,300	1.49	823,300	12/31/2011
Fort Washington Investment Advisors, Inc.	796,071	1.44	-41,618	12/31/2011
Dreyfus Investment Advisors, Inc.	791,600	1.43	14,600	12/31/2011
Bluefin Investment Management	731,600	1.33	424,000	12/31/2011
Turner Investment Partners, Inc.	724,833	1.31	472,533	12/31/2011
OppenheimerFunds, Inc.	713,825	1.29	164,585	12/31/2011
Neuberger Berman LLC	695,493	1.26	92,193	12/31/2011
Adage Capital Advisors LLC	650,000	1.18	-194,394	12/31/2011
Capital World Investors	639,000	1.16	233,000	12/31/2011
Northern Trust Investments	596,190	1.08	2,724	12/31/2011
Loomis, Sayles & Co. LP	583,728	1.06	266,231	12/31/2011
TIAA-CREF Asset Management LLC	545,718	0.99	-9,316	12/31/2011

Ownership data is provided by FactSet, a third party service, and NxStage Medical, Inc. does not maintain or provide information directly to this service.