Exhibit 5.1

November 4, 2005

CNS, Inc.
7615 Smetana Lane
Eden Prairie, Minnesota 55344

Re: Opinion of Counsel as to Legality of 1,200,000 shares of Common Stock to be
Registered under the Securities Act of 1933

Ladies and Gentlemen:

        This opinion is furnished in connection with the registration under the Securities Act of 1933 on Form S-8 of 1,200,000 shares of Common Stock, $.01 par value per share, of CNS, Inc., (the “Company”) offered to employees of the Company or its subsidiaries pursuant to the CNS, Inc. 2000 Stock Option Plan (the “Plan”).

        As general counsel for the Company, we advise you that it is our opinion, based on our familiarity with the affairs of the Company and upon our examination of pertinent documents, that the 1,200,000 shares of Common Stock to be offered to officers, employees, consultants and members of the Board of Directors by the Company under the Plan will, when paid for and issued, be validly issued and outstanding, fully paid and nonassessable shares of Common Stock of the Company.

        The undersigned hereby consent to the filing of this opinion with the Securities and Exchange Commission as an Exhibit to the Registration Statement with respect to said shares of Common Stock under the Securities Act of 1933.

Very truly yours,

LINDQUIST & VENNUM P.L.L.P.

/s/   Lindquist & Vennum P.L.L.P.