<PAGE>

                                                                  EXHIBIT - 31.1

                                  MOSSIMO, INC.

                  CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICER


         I, Mossimo Giannulli, certify that:

         1.   I have reviewed this quarterly report on Form 10-Q of Mossimo,
              Inc.;

         2.   Based on my knowledge, this 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 financial statements, and other
              financial information included in this 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 are responsible
              for establishing and maintaining disclosure controls and
              procedures (as defined in Exchange Act Rules 13a-15(e)(4) and
              15d-15(e)(4)) for the registrant and 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;

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

              (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.

DATED:  May 14, 2004
                                       /s/ MOSSIMO GIANNULLI
                                       -----------------------------------------
                                       Mossimo Giannulli
                                       Chairman and Chief Executive Officer