Exhibit 5.1





                                  September 2, 1998





          U.S. Securities and Exchange Commission
          450 Fifth Street, N.W.
          Washington, DC 20549  

               Re:  VASCO Data Security International, Inc.--Registration
          Statement on Form S-8

          Ladies and Gentlemen:

               We have acted as securities counsel for VASCO Data Security
          International, Inc., a Delaware corporation (the "Company"), in
          connection with the preparation by the Company of a Registration
          Statement on Form S-8 (the "Registration Statement") under the
          Securities Act of 1933 relating to the registration of 5,000,000
          shares (the "Shares") of the Company's Common Stock, par value
          $0.001 per share (the "Common Stock"), which may be offered from
          time to time by the Company.

               In connection with the preparation of the Registration
          Statement, we have examined such documents, instruments, records,
          certificates and matters as we have considered appropriate and
          necessary to render this opinion.  We have assumed for the
          purpose of this opinion the authenticity of all documents
          submitted to us as originals and the conformity with the
          originals of all documents submitted to us as copies, and the
          genuineness of all signatures thereon.

               Based on the foregoing and in reliance thereon, it is our
          opinion that the issuance of the Shares have been duly authorized
          and, after the Registration Statement becomes effective and after
          any post-effective amendment required by law is duly completed,
          filed and becomes effective (such Registration Statement as it
          become effective, or, if required to be post-effectively amended,
          then as it is so amended, is referred to hereinafter as the
          "Final Registration Statement"), and when the applicable
          provisions of "Blue Sky" or other state securities laws shall
          have been complied with, and when the options are duly exercised
          and Shares are issued and/or sold in accordance with the terms
          described in the prospectus forming a part of the Final
          Registration Statement, the Shares will be validly issued, fully
          paid and nonassessable.

               We hereby consent to the inclusion of our opinion as Exhibit
          5.1 to the Registration Statement and further consent to the
          references to this firm in the Registration Statement.  In giving
          this consent, we do not hereby admit that we are in the category
          of persons whose consent is required under Section 7 of the
          Securities Act of 1933 or the rules and regulations of the
          Commission thereunder.

               This opinion is rendered solely for your benefit in
          accordance with the subject transaction and is not to be
          otherwise used, circulated, quoted or referred to without our
          prior written consent.  This opinion is limited to the laws of
          the State of Delaware and the federal laws of the United States.


                                             Very truly yours,



                                             /s/
                                   SCHNADER HARRISON SEGAL & LEWIS LLP