<PAGE>

                                                                    EXHIBIT 31.2

                                  CERTIFICATION

I, Todd E. Simpson, certify that:

1.   I have reviewed this quarterly report on Form 10-Q of Targeted Genetics
     Corporation;

2.   Based on my knowledge, this quarterly report does not contain any untrue
     statement of a material fact or omit to state a material fact necessary to
     make the statements made, in light of the circumstances under which such
     statements were made, not misleading with respect to the period covered by
     this report;

3.   Based on my knowledge, the condensed consolidated financial statements, and
     other financial information included in this quarterly report, fairly
     present in all material respects the financial condition, results of
     operations and cash flows of the registrant as of, and for, the periods
     presented in this report;

4.   The registrant's other certifying officer and I am responsible for
     establishing and maintaining disclosure controls and procedures (as defined
     in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and we
     have:

     a)   Designed such disclosure controls and procedures, or caused such
          disclosure controls and procedures to be designed under our
          supervision, to ensure that material information relating to the
          registrant, including its consolidated subsidiaries, is made known to
          us by others within those entities, particularly during the period in
          which this report is being prepared;

     b)   Evaluated the effectiveness of the registrant's disclosure controls
          and procedures and presented in this report our conclusions about the
          effectiveness of the disclosure controls and procedures, as of the end
          of the period covered by this report based on such evaluation; and

     c)   Disclosed in this report any change in the registrant's internal
          control over financial reporting that occurred during the registrant's
          most recent fiscal quarter (the registrant's fourth fiscal quarter in
          the case of an annual report) that has materially affected, or is
          reasonably likely to materially affect, the registrant's internal
          control over financial reporting; and

5.   The registrant's other certifying officer and I have disclosed, based on
     our most recent evaluation, to the registrant's auditors and the audit
     committee of the registrant's board of directors (or persons performing the
     equivalent function):

     a)   all significant deficiencies and material weaknesses in the design or
          operation of internal control over financial reporting which are
          reasonably likely to adversely affect the registrant's ability to
          record, process, summarize and report financial information; and

     b)   any fraud, whether or not material, that involves management or other
          employees who have a significant role in the registrant's internal
          control over financial reporting.

July 31, 2003                  /s/ TODD E. SIMPSON
Date                           -------------------------------------------------
                               Todd E. Simpson
                               Vice President, Finance and Administration, Chief
                               Financial Officer, Secretary and Treasurer
                               (Principal Financial and Accounting Officer)