EXHIBIT 5.1

January 21, 2005

RITA Medical Systems, Inc.

967 N. Shoreline Blvd.

Mountain View, CA 94043

Registration Statement on Form S-3/A (File No. 333-121013)

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-3/A (File No. 333-121013) (the “Registration Statement”) to be filed by you with the Securities and Exchange Commission on or about January 21, 2005, in connection with the registration under the Securities Act of 1933 of shares of your Common Stock (the “Shares”). As your legal counsel in connection with this transaction, we have examined the proceedings taken and we are familiar with the proceedings proposed to be taken by you in connection with the sale and issuance of the Shares.

It is our opinion that the Shares, when issued and sold in the manner described in the Registration Statement, will be legally and validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration Statement and further consent to the use of our name wherever it appears in the Registration Statement and in any amendment to it.

Sincerely,

/s/ Heller Ehrman White & McAuliffe LLP

MBW