Exhibit 32.2

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report on Form 10-Q of NxStage Medical, Inc. (the “Company”) for the period ended March 31, 2012 as filed with the Securities and Exchange Commission on the date hereof (this “report”), I, Robert S. Brown, Chief Financial Officer and Senior Vice President of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to my knowledge:

 

  (1) This report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

 

  (2) The information contained in this report fairly presents, in all material respects, the financial condition and results of operations of the Company.

 

/s/ Robert S. Brown

Robert S. Brown

Chief Financial Officer and Senior Vice President
Date: May 8, 2012