NxStage® Achieves Milestone with 1,000 Patients Receiving Therapy

NxStage® Achieves Milestone with 1,000 Patients Receiving Therapy *

Adoption of First Truly Portable Home Hemodialysis Machine More Than Triples in 2006

LAWRENCE, MA., December 1, 2006, NxStage Medical, Inc. (NASDAQ: NXTM), announced that over 1,000 patients are now using its NxStage® System OneTM, the first truly portable home hemodialysis machine. This latest milestone more than triples the number of patients benefiting from NxStage therapy at the end of 2005. Clinicians in more than 150 markets across the United States now offer daily home hemodialysis with the NxStage System One to their patients. NxStage Medical will continue to broaden its roll-out of the System One, which was recently recognized by the Wall Street Journal’s Global Technology Innovation Awards.

“In steadily growing numbers, patients, their families and clinicians are responding enthusiastically to their experience with the NxStage System One,” said Jeff Burbank, President and Chief Executive Officer, NxStage Medical. “This response validates our belief that simple, patient-friendly technology can significantly grow the number of patients who may realize the health and quality of life benefits of home-based therapy. In a very short time, we believe that we have helped increase by over 50% the total number of patients that receive hemodialysis therapy at home in the United States. Clearly, NxStage could not have accomplished this latest milestone without the dedicated support of our strong partner providers and clinicians, and the trust of our patients. On behalf of the rest of our team, I’d like to personally thank those who have worked and grown with us since our early clinical trial days, for their commitment to patient care and their confidence in the NxStage System.”*

“The availability of viable home treatment options is imperative as the number of dialysis patients continues to grow, and the home presents a natural setting to capture the clinical benefits of more frequent and/or longer dialysis therapies,” said John Moran, M.D., Corporate Medical Director for Wellbound, a leading home dialysis therapy provider. “Our program became involved with NxStage three years ago during NxStage’s initial clinical trials, and we have been delighted with the lasting clinical and quality-of-life benefits observed as we offer home daily therapy with the System One to more and more patients.”

The NxStage System One is the first truly portable hemodialysis system cleared for home use by the FDA. Unlike traditional dialysis equipment, the System One plugs into standard electrical outlets, requires no special infrastructure to operate and is easy to use by trained patients accompanied by their trained partners. Rather than commuting to and from a dialysis clinic three times per week for scheduled treatment sessions lasting three to four hours, patients who use the NxStage® System OneTM have the personal freedom to conduct prescribed treatments at home on their own schedule and to bring the System with them when they travel.

Patients using the System One generally perform dialysis treatments on a more frequent basis. A growing body of peer-reviewed literature documents that more frequent therapy results in clinical benefits such as increased energy levels and being able to reduce or eliminate certain medications. NxStage Medical also recently received FDA clearance in April 2006 for its PureFlowTM SL, a compact, easy-to-use system that prepares high-purity dialysate from regular tap water, helping to make daily home hemodialysis even more practical and accessible to patients. The PureFlow SL eliminates the need for bagged dialysate in the home, while still allowing patients to use the bagged system when they travel.

NxStage Medical also provides a version of the System One for treatment of acute renal failure in the critical care setting to more than 60 of the leading institutions across the country, including The University of Chicago Hospitals, Rush University Medical Center, and others. When critical care and home therapy experiences are combined, over 250,000 treatments have been administered, representing over 1 million hours of therapy experience with the NxStage System One.*

About NxStage Medical ******

NxStage Medical, Inc. (NASDAQ: NXTM) is a medical device company, headquartered in Lawrence, Massachusetts, USA, that develops, manufactures and markets innovative dialysis systems for the treatment of end-stage renal disease, or ESRD, and acute kidney failure. For more information on NxStage and its products, please visit the company’s website at http://www.nxstage.com/>www.nxstage.com.

About End-Stage Renal Disease

End-stage renal disease is the permanent failure of the kidneys to filter the body’s wastes. It is most commonly caused by diabetes, hypertension, or genetic disorders. In order to survive, ESRD patients must use some form of therapy to replace the function of the kidneys for the rest of their lives. Currently, over 450,000 patients in the United States suffer from ESRD, and the costs of treating ESRD patients are over $20 billion annually in the U.S. Due to increases in diabetes, hypertension, and the aging of the U.S. population, those figures are projected to double within the next 10-15 years. The most common form of kidney replacement therapy in the United States today is hemodialysis, which is used by over 350,000 patients. The great majority of these patients are treated with conventional, in-center hemodialysis, in which they must travel to a nearby dialysis center three times per week, where they are connected to dialysis machines for treatments lasting approximately three to four hours, to cleanse their blood.*

About Hemodialysis

Today, most patients undergo hemodialysis therapy three times a week in outpatient dialysis centers. This differs significantly from the 24/7 workings of the naturally functioning kidney. Increasingly, clinicians and patients have recognized opportunities for therapy improvements with more frequent, or daily, dialysis. Hundreds of clinical papers have reported on the health and quality of life benefits of hemodialysis done more frequently. The reported benefits include reduced hypertension, reduced cardiac strain and left ventricular hypertrophy, reduced amyloid disease, and improved anemia status, appetite, and quality of life, including the ability to return to work. A summary of the literature discussing these benefits can be found on NxStage’s website, http://www.nxstage.com/>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 home dialysis products, including NxStage’s products, the expected growth in ESRD patients, and the expected benefits of home and more frequent therapies. 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 the NxStage System One, growth in home hemodialysis, 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 quarter ended September 30, 2006. **NxStage is under no obligation to (and expressly disclaims any such obligation to) update or alter its forward-looking statements, whether as a result of new information, future events or otherwise.