Exhibit 99.1

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

Highlights:

- Revenue Increases to $53.8 million, up 22% from Q2’10

- Home Market Increases to $27.0 million, up 30% from Q2’10

- Gross Margin Increases to 35%, up from 31% in Q2’10

- Company Announces Extension of Agreement in the Home Market with Large Customer

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

Revenue for the second quarter of 2011 increased to $53.8 million, an increase of 22 percent when compared with revenue of $44.0 million for the second quarter of 2010. The increase was driven by strong performance across all three markets: Home, Critical Care and In-Center.

The Company grew Home revenue to $27.0 million for the second quarter of 2011, representing an increase of 30 percent when compared with revenue of $20.8 million for the second quarter of 2010. Critical Care revenue grew to $8.6 million for the second quarter of 2011, representing an increase of 29 percent when compared with revenue of $6.7 million for the second quarter of 2010. Revenue in the In-Center market, from the Company’s Medisystems business, increased to $18.2 million for the second quarter of 2011, representing an increase of 10 percent when compared with revenue of $16.5 million for the second quarter of 2010.

“Building on last quarter’s momentum, we delivered strong results across our business and topped expectations,” stated Jeffrey H. Burbank, CEO of NxStage Medical, Inc. “With the first and only truly portable hemodialysis system cleared for home use by the FDA and similar competition still a number of years away, we see significant opportunities for growth, continued innovation and expansion within the Home. Given the strength that we’re seeing across all markets and the growth in our opportunity pipeline, we’re raising our revenue outlook for 2011 to a range of $210 million to $215 million.”

NxStage reported a net loss of $5.6 million, or ($0.10) per share, for the second quarter of 2011 compared with a net loss of $8.3 million, or ($0.17) per share, for the second quarter of 2010.

For the second 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 $1.8 million, compared with an Adjusted EBITDA loss of $0.2 million in the second quarter of 2010. (See the exhibits for a reconciliation of this non-GAAP measure.)

NxStage announced that it recently concluded its renegotiation of its United States home market agreement with one of its largest customers and signed an amendment to that agreement, extending the term to December 31, 2012, and up to one additional year thereafter. The amended agreement covers the use of NxStage’s products for home hemodialysis.

Separately, NxStage announced that pursuant to its agreement with DaVita, for the period ended June 30, 2011, DaVita achieved System One home patient growth targets that entitled it to become vested in warrants to purchase 250,000 shares of NxStage common stock.

Guidance:

For the third quarter of 2011, the Company is forecasting revenue to be within a range of $53.5 to $54.5 million. At this revenue level, the Company would expect a net loss in the range of $5.0 to $6.0 million or ($0.09) to ($0.11) per share, and Adjusted EBITDA in the range of $1.0 to $2.0 million for the third quarter of 2011.

Supported by its strong performance in the first half of 2011, the Company now anticipates revenue for the 2011 fiscal year to be in a range of $210 to $215 million, compared with its prior guidance for revenues to be in a range of $205 to $213 million. The Company is maintaining its guidance for 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. As a result of the impact of unfavorable foreign exchange and the acceleration of the transition of our blood tubing sets to in-house manufacturing, the Company expects fourth quarter gross margin percentage to be at around the low end of its previously announced guidance of 38 to 42 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 second quarter financial results. To listen to the conference call, please dial 800.510.9836 (domestic) or 617.614.3670 (international). The passcode is 68598834. 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 August 10, 2011. To access the replay dial 888-286-8010 (domestic) or 617-801-6888 (international) and enter passcode 87428332. 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., 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 March 31, 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								Six Months Ended
		June 30,								June 30,
		2011				2010				2011				2010
Revenues		$	53,768			$	44,008			$	104,332			$	84,416
Cost of revenues			34,903				30,246				67,434				58,841
Gross profit			18,865				13,762				36,898				25,575
Operating expenses:
Selling and marketing			9,369				8,565				18,579				16,582
Research and development			3,589				3,202				7,306				6,237
Distribution			4,431				3,632				8,589				7,043
General and administrative			5,460				5,643				11,042				10,581
Total operating expenses			22,849				21,042				45,516				40,443
Loss from operations			(3,984	)			(7,280	)			(8,618	)			(14,868	)
Other expense:
Interest expense			(1,170	)			(1,148	)			(2,327	)			(2,256	)
Other (expense) income, net			(170	)			330				(196	)			213
			(1,340	)			(818	)			(2,523	)			(2,043	)
Net loss before income taxes			(5,324	)			(8,098	)			(11,141	)			(16,911	)
Provision for income taxes			226				158				419				344
Net loss		$	(5,550	)		$	(8,256	)		$	(11,560	)		$	(17,255	)
Net loss per share, basic and diluted		$	(0.10	)		$	(0.17	)		$	(0.22	)		$	(0.37	)
Weighted-average shares outstanding, basic and diluted			54,014				47,492				53,716				47,228

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

		June 30,				December 31,
		2011				2010
ASSETS
Current assets:
Cash and cash equivalents		$	100,426			$	104,339
Accounts receivable, net			15,889				14,107
Inventory			39,213				34,950
Prepaid expenses and other current assets			2,475				2,084
Total current assets			158,003				155,480
Property and equipment, net			12,540				8,290
Field equipment, net			13,036				13,660
Deferred cost of revenues			40,458				40,081
Intangible assets, net			24,013				25,412
Goodwill			42,698				42,698
Other assets			675				473
Total assets		$	291,423			$	286,094
LIABILITIES AND STOCKHOLDERS’ EQUITY
Current liabilities:
Accounts payable		$	22,620			$	16,811
Accrued expenses			14,201				19,537
Current portion of long-term debt			16				43
Total current liabilities			36,837				36,391
Deferred revenues			55,995				55,366
Long-term debt			41,818				40,454
Other long-term liabilities			5,639				1,754
Total liabilities			140,289				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 June 30, 2011 and December 31, 2010			—				—
Common stock: par value $0.001, 100,000,000 shares authorized; 55,172,136 and 54,043,317 shares issued as of June 30, 2011 and December 31, 2010, respecitvely			55				53
Additional paid-in capital			479,186				465,642
Accumulated deficit			(319,986	)			(308,426	)
Accumulated other comprehensive income			395				85
Treasury stock, at cost: 480,923 and 325,104 shares as of June 30, 2011 and December 31, 2010, respectively			(8,516	)			(5,225	)
Total stockholders’ equity			151,134				152,129
Total liabilities and stockholders’ equity		$	291,423			$	286,094

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

		Six Months Ended
		June 30,
		2011				2010
Cash flows from operating activities:
Net loss		$	(11,560	)		$	(17,255	)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization			11,459				11,077
Stock-based compensation			6,701				6,875
Other			1,737				1,128
Changes in operating assets and liabilities:
Accounts receivable			(1,753	)			(527	)
Inventory			(13,363	)			(13,327	)
Prepaid expenses and other assets			(546	)			(404	)
Accounts payable			5,471				(399	)
Accrued expenses and other liabilities			(2,446	)			3,060
Deferred revenues			629				8,745
Net cash used in operating activities		$	(3,671	)		$	(1,027	)

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

		Three Months Ended								Six Months Ended
		June 30,								June 30,
		2011				2010				2011				2010
System One segment
Home		$	27,013			$	20,815			$	53,058			$	39,858
Critical Care			8,591				6,652				16,029				12,711
Total System One segment			35,604				27,467				69,087				52,569
In-Center segment			18,164				16,541				35,245				31,847
Total		$	53,768			$	44,008			$	104,332			$	84,416

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

		Three Months Ended								Six Months Ended
		June 30,								June 30,
		2011				2010				2011				2010
Net loss		$	(5.6	)		$	(8.3	)		$	(11.6	)		$	(17.3	)
Less: Depreciation, amortization, interest, and taxes			7.3				6.5				14.4				13.4
Less: Adjusting items*			0.1				1.6				0.1				2.4
Adjusted EBITDA gain (loss)		$	1.8			$	(0.2	)		$	2.9			$	(1.5	)

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

		Three Months Ended
		September 30, 2011
		High				Low
		Estimate				Estimate
Net loss		$	(5.0	)		$	(6.0	)
Less: Depreciation, amortization, interest, and taxes			6.9				6.9
Less: Adjusting items*			0.1				0.1
Adjusted EBITDA gain		$	2.0			$	1.0