Exhibit 99.1

NXSTAGE REPORTS RECORD FOURTH QUARTER AND FULL-YEAR 2011 FINANCIAL RESULTS; REVENUE GROWTH EXCEEDS COMPANY GUIDANCE

Highlights:

LAWRENCE, Mass., February 29, 2012 — NxStage^® Medical, Inc. (Nasdaq: NXTM), a leading manufacturer of innovative dialysis products, today reported record financial results for the three and twelve months ended December 31, 2011, that includes revenue above the top end of its guidance range.

Revenue for the full-year 2011 increased 21 percent to $217.3 million, compared with revenue of $179.2 million for the full-year 2010. Revenue for the fourth quarter of 2011 increased 15 percent to a record $57.0 million compared with revenue of $49.8 million for the fourth quarter of 2010. The increase in both periods was led by the Company’s solid performance in the Home market as a result of growing adoption of more frequent home hemodialysis with the NxStage System One™.

Home delivered 27 percent annual growth, with revenue increasing to $108.5 million for the full-year 2011 compared with revenue of $85.8 million for the full-year 2010. Home revenue increased to $28.2 million in the fourth quarter of 2011 compared with revenue of $23.6 million in the fourth quarter of 2010, representing a 20 percent increase.

“Home revenue continued to show strength both on an annual and sequential basis,” stated Jeffrey H. Burbank, Chief Executive Officer of NxStage Medical, Inc. “The majority of Home’s sequential revenue growth in Q4 was driven by our performance in the U.S. which was in-line with normal seasonality and slightly better than our guidance.”

Critical Care delivered 25 percent annual growth, with revenue increasing to $35.0 million for the full-year 2011 compared with revenue of $28.1 million for the full-year 2010. Revenue in Critical Care increased to $9.8 million in the fourth quarter of 2011, compared with revenue of $8.6 million in the fourth quarter of 2010, representing a 14 percent increase.

The Company’s in-center business, Medisystems, delivered 13 percent annual growth with revenue increasing to $73.8 million for the full-year 2011, compared with revenue of $65.4 million for the full-year 2010. Fourth quarter revenue was $19.0 million, compared with $17.6 million in the fourth quarter of 2010.

“NxStage delivered another year of solid growth in 2011. This performance is clear evidence of the strategic progress we continue to make across our business. We achieved both our financial and business objectives and advanced our mission to improve the lives of patients with ESRD,” stated Burbank.

Burbank continued, “Entering 2012, I believe that we have good underlying market fundamentals, a strong balance sheet, a solid operating model, as well as the deepest product pipeline in our Company’s history. We see significant opportunities to advance our long term growth strategy and remain confident in our ability to deliver continued improvement and meaningful growth.”

In commenting on UnitedHealthcare’s recent policy update in support of reimbursement for more frequent home hemodialysis Burbank stated, “We applaud UnitedHealthcare for their leadership in providing greater access to the life changing benefits possible with our therapy. This is an exciting and important step forward in our efforts to make reimbursement simple, predictable and appropriate across all payers, including Medicare.”

NxStage reported a net loss of $21.4 million or ($0.39) per share for the full-year 2011 compared with a net loss of $31.7 million or ($0.66) per share for the full-year 2010. The Company reported a net loss of $4.6 million or ($0.08) per share for the fourth quarter of 2011 compared with a net loss of $6.3 million or ($0.13) per share for the fourth quarter of 2010.

For the full-year 2011, the Company reported Adjusted EBITDA, adjusted for stock-based compensation, deferred revenue recognized, manufacturing transition costs and other non-cash expenses, of $7.3 million, compared with $0.5 million for the full-year 2010. For the fourth quarter of 2011, Adjusted EBITDA was $2.0 million compared with $1.5 million in the fourth quarter of 2010. (See the exhibits for a reconciliation of this non-GAAP measure.)

Guidance:

For the first quarter of 2012, the Company is forecasting revenue to be between $56.0 million and $57.0 million, 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 full fiscal year 2012, the Company is forecasting revenue to be between $240 million and $245 million, a net loss in the range of $14.0 to $18.0 million or ($0.25) to ($0.32) per share, and Adjusted EBITDA in the range of $8.0 million to $12.0 million. The Company expects to achieve consolidated gross margins of between 39 percent to 43 percent in the fourth quarter of 2012.

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, Wednesday, February 29, 2012, at 9:00 a.m. Eastern Time to discuss its fourth quarter and year-end 2011 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.

A replay of the conference call will be available 2 hours after the completion of the call through March 14, 2012. To access the replay, dial 855- 859-2056 (domestic) or 404- 537-3406 (international) and reference conference ID 45478602. An online archive of the conference call can be accessed via the investor relations section of the Company’s website at www.nxstage.com.

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 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 September 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.

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.

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Consolidated Statements of Operations

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Cash Flows from Operating Activities

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Revenues by Segment

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Non-GAAP Financial Measures

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Non-GAAP Financial Guidance

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