Exhibit 99.1

NxStage Reports Record Third Quarter 2011 Financial Results and Raises Revenue
Guidance For 2011

Highlights:

- Revenue Increases to $55.9 million, up 24% from Q3’10

- Home Market Increases to $27.2 million, up 22% from Q3’10

- Gross Margin Increases to 35%, up from 33% in Q3’10

LAWRENCE, Mass., November 3, 2011 — NxStage Medical, Inc. (Nasdaq: NXTM), a leading manufacturer of innovative dialysis products, today reported record financial results for the third quarter ended September 30, 2011, with total revenue well above the top end of its guidance range.

Revenue for the third quarter of 2011 increased to $55.9 million, an increase of 24 percent when compared with revenue of $45.0 million for the third quarter of 2010. The growth was driven by strong operating performance across the Company’s business.

The Company grew Home revenue to $27.2 million for the third quarter of 2011, representing an increase of 22 percent when compared with revenue of $22.3 million for the third quarter of 2010. Critical Care revenue grew to $9.2 million for the third quarter of 2011, representing an increase of 35 percent when compared with revenue of $6.8 million for the third quarter of 2010. Revenue for In-Center, from the Company’s Medisystems business, increased to $19.5 million for the third quarter of 2011, representing an increase of 23 percent when compared with revenue of $15.9 million for the third quarter of 2010.

“Not only was this a record quarter with respect to revenues, but also one where we made meaningful progress in advancing metrics across our business,” stated Jeffrey H. Burbank, CEO of NxStage Medical, Inc. “These results are strong validation of our business model and we see significant opportunities across our business to advance our long term growth strategy. We are particularly pleased with the growing strength of clinical data showing that patients benefit from more frequent hemodialysis and that they live longer and healthier lives.”

NxStage reported a net loss of $5.3 million, or ($0.10) per share, for the third quarter of 2011 compared with a net loss of $8.2 million, or ($0.17) per share, for the third quarter of 2010.

For the third quarter of 2011, the Company reported Adjusted EBITDA, adjusted for stock-based compensation, deferred revenue recognized, manufacturing transition costs and other non-cash expenses of $2.4 million, compared with an Adjusted EBITDA of $0.5 million in the third quarter of 2010. (See the exhibits for a reconciliation of this non-GAAP measure.)

Guidance:

For the fourth quarter of 2011, the Company is forecasting revenue to be within a range of $55.5 to $56.5 million. At this revenue level, the Company would expect a net loss in the range of $4.5 to $5.5 million or ($0.08) to ($0.10) per share, and Adjusted EBITDA in the range of $1.5 to $2.5 million for the fourth quarter of 2011.

The Company’s fourth quarter revenue guidance translates to an upward revision of the Company’s annual guidance, putting expected revenue above the top end of its previous range. The Company now expects annual revenue to be within a range of $216 to $217 million compared with previous guidance for revenue to be within a range of $210 to $215 million. The Company continues to expect a net loss in the range of $19 to $23 million or ($0.36) to ($0.43) per share, and for Adjusted EBITDA to be in the range of $6.0 million to $10.0 million for the 2011 fiscal year. The Company expects the fourth quarter gross margin percentage to be between 37 and 38 percent.

This release contains a non-GAAP financial measure. A reconciliation of the Company’s non-GAAP financial measure to its most comparable GAAP financial measure is in the exhibits to this press release.

Conference Call:

NxStage will also host a conference call today at 9:00 a.m. Eastern Time to discuss its third quarter financial results. To listen to the conference call, please dial 877-392-9886 (domestic) or 707-287-9329 (international). The call will also be webcast LIVE and can be accessed via the investor relations section of the Company’s website at www.nxstage.com/ir.cfm.

A replay of the conference call will be available 2 hours after the conclusion of the call through November 17, 2011. To access the replay dial 855-859-2056 (domestic) or 404-537-3406 (international). The conference ID is 17404745. An online archive of the conference call can be accessed via the investor relations section of the Company’s website at www.nxstage.com/ir.cfm.

About NxStage

NxStage Medical, Inc. (Nasdaq: NXTM) is a medical device company, headquartered in Lawrence, Massachusetts, USA, that develops, manufactures and markets innovative products for the treatment of ESRD and acute kidney failure. For more information on NxStage and its products, please visit the company’s website at www.nxstage.com.

Forward-Looking Statements

This release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this release that are not clearly historical in nature are forward-looking, and the words “anticipate,” “believe,” “expect,” “estimate,” “plan,” and similar expressions are generally intended to identify forward-looking statements. Examples of these forward-looking statements include statements as to the anticipated demand for the Company’s products, anticipated operating results, including revenues, loss, gross margin and Adjusted EBITDA numbers, and other expectations as to future operating results. All forward-looking statements involve risks, uncertainties and contingencies, many of which are beyond NxStage’s control, which may cause actual results, performance, or achievements to differ materially from anticipated results, performance or achievements, including market acceptance and demand for NxStage’s products, growth in home and/or daily hemodialysis, unanticipated difficulties in achieving operational efficiencies and cost reductions,

changes in reimbursement for home and daily hemodialysis, changes in the regulatory environment, changes in the historical purchasing patterns and preferences of our customers, including DaVita Inc., Fresenius, and certain other factors that may affect future operating results and which are detailed in NxStage’s filings with the Securities and Exchange Commission, including its Quarterly Report on Form 10-Q for the period ended June 30, 2011.

In addition, the statements in this press release represent NxStage’s expectations and beliefs as of the date of this press release. NxStage anticipates that subsequent events and developments may cause these expectations and beliefs to change. However, while NxStage may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so, whether as a result of new information, future events, or otherwise. These forward-looking statements should not be relied upon as representing NxStage’s expectations or beliefs as of any date subsequent to the date of this press release.

Contact:

Kristen K. Sheppard, Esq.

VP, Investor Relations

ksheppard@nxstage.com

Non-GAAP Financial Measure

The Company discloses a certain non-GAAP financial measure to supplement the Company’s consolidated financial statements presented on a GAAP basis. This non-GAAP measure is not in accordance with, or an alternative for, generally accepted accounting principles in the United States and may be different from similar non-GAAP financial measures used by other companies. The non-GAAP financial measure disclosed by the Company is not meant to be considered superior to or a substitute for results of operations prepared in accordance with GAAP. Management uses Adjusted EBITDA (EBITDA adjusted for stock based-compensation, deferred revenue recognized, manufacturing transition costs and other non-cash expenses) to understand operational cash usage. The Company believes the non-GAAP financial measure provides useful and supplementary information allowing investors greater transparency to one measure used by management. The non-GAAP financial measure is meant to supplement, and to be viewed in conjunction with, GAAP financial measures. The non-GAAP financial measure is reconciled to the most comparable GAAP financial measure below.

NxStage Medical, Inc.
Condensed Consolidated Statements of Operations
(in thousands, except per share data)
(unaudited)

		Three Months Ended								Nine Months Ended
		September 30,								September 30,
		2011				2010				2011				2010
Revenues		$	55,903			$	45,033			$	160,235			$	129,449
Cost of revenues			36,363				30,073				103,797				88,914
Gross profit			19,540				14,960				56,438				40,535
Operating expenses:
Selling and marketing			9,446				8,452				28,025				25,034
Research and development			3,388				3,132				10,694				9,369
Distribution			4,709				3,788				13,298				10,831
General and administrative			5,708				6,023				16,750				16,604
Total operating expenses			23,251				21,395				68,767				61,838
Loss from operations			(3,711	)			(6,435	)			(12,329	)			(21,303	)
Other expense:
Interest expense			(1,186	)			(1,176	)			(3,513	)			(3,432	)
Other (expense), net			(146	)			(341	)			(342	)			(128	)
			(1,332	)			(1,517	)			(3,855	)			(3,560	)
Net loss before income taxes			(5,043	)			(7,952	)			(16,184	)			(24,863	)
Provision for income taxes			235				212				654				556
Net loss		$	(5,278	)		$	(8,164	)		$	(16,838	)		$	(25,419	)
Net loss per share, basic and diluted		$	(0.10	)		$	(0.17	)		$	(0.31	)		$	(0.54	)
Weighted-average shares outstanding, basic and diluted			54,428				48,049				53,953				47,501

NxStage Medical, Inc.
Condensed Consolidated Balance Sheets
(in thousands, except share data)
(unaudited)

		September 30,				December 31,
		2011				2010
ASSETS
Current assets:
Cash and cash equivalents		$	101,247			$	104,339
Accounts receivable, net			17,497				14,107
Inventory			35,563				34,950
Prepaid expenses and other current assets			3,104				2,084
Total current assets			157,411				155,480
Property and equipment, net			14,276				8,290
Field equipment, net			12,718				13,660
Deferred cost of revenues			41,355				40,081
Intangible assets, net			23,314				25,412
Goodwill			42,698				42,698
Other assets			1,497				473
Total assets		$	293,269			$	286,094
LIABILITIES AND STOCKHOLDERS’ EQUITY
Current liabilities:
Accounts payable		$	19,195			$	16,811
Accrued expenses			16,265				19,537
Current portion of long-term debt			—				43
Total current liabilities			35,460				36,391
Deferred revenues			56,682				55,366
Long-term debt			42,521				40,454
Other long-term liabilities			6,994				1,754
Total liabilities			141,657				133,965
Commitments and contingencies
Stockholders’ equity:
Undesignated preferred stock: par value $0.001, 5,000,000 shares authorized; no shares issued and outstanding as of September 30, 2011 and December 31, 2010			—				—
Common stock: par value $0.001, 100,000,000 shares authorized; 55,617,552 and 54,043,317 shares issued as of September 30, 2011 and December 31, 2010, respectively			55				53
Additional paid-in capital			485,191				465,642
Accumulated deficit			(325,264	)			(308,426	)
Accumulated other comprehensive income			146				85
Treasury stock, at cost: 480,923 and 325,104 shares as of September 30, 2011 and December 31, 2010, respectively			(8,516	)			(5,225	)
Total stockholders’ equity			151,612				152,129
Total liabilities and stockholders’ equity		$	293,269			$	286,094

NxStage Medical, Inc.
Cash Flows from Operating Activities
(in thousands)
(unaudited)

		Nine Months Ended
		September 30,
		2011				2010
Cash flows from operating activities:
Net loss		$	(16,838	)		$	(25,419	)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization			17,415				16,879
Stock-based compensation			10,166				10,985
Other			2,387				1,750
Changes in operating assets and liabilities:
Accounts receivable			(3,414	)			(303	)
Inventory			(15,196	)			(20,504	)
Prepaid expenses and other assets			(2,067	)			(327	)
Accounts payable			2,296				(3,376	)
Accrued expenses and other liabilities			195				3,980
Deferred revenues			1,316				14,087
Net cash used in operating activities		$	(3,740	)		$	(2,248	)

NxStage Medical, Inc.
Revenues by Segment
(in thousands)

		Three Months Ended								Nine Months Ended
		September 30,								September 30,
		2011				2010				2011				2010
System One segment
Home		$	27,218			$	22,346			$	80,276			$	62,204
Critical Care			9,170				6,817				25,199				19,528
Total System One segment			36,388				29,163				105,475				81,732
In-Center segment			19,515				15,870				54,760				47,717
Total		$	55,903			$	45,033			$	160,235			$	129,449

NxStage Medical, Inc.
Non-GAAP Financial Measures
(in millions)
(unaudited)

		Three Months Ended								Nine Months Ended
		September 30,								September 30,
		2011				2010				2011				2010
Net loss		$	(5.3	)		$	(8.2	)		$	(16.8	)		$	(25.4	)
Less: Depreciation, amortization, interest, and taxes			7.5				7.6				21.9				21.0
Less: Adjusting items*			0.2				1.1				0.2				3.4
Adjusted EBITDA gain (loss)		$	2.4			$	0.5			$	5.3			$	(1.0	)

NxStage Medical, Inc.
Non-GAAP Financial Guidance
(amounts in millions)

		Three Months Ended
		December 31, 2011
		High				Low
		Estimate				Estimate
Net loss		$	(4.5	)		$	(5.5	)
Less: Depreciation, amortization, interest, and taxes			7.3				7.3
Less: Adjusting items*			(0.3	)			(0.3	)
Adjusted EBITDA gain		$	2.5			$	1.5