A retrospective evaluation of 83 patients with Reiter's syndrome (RS) and 166 comparison arthritis patients was conducted in order to assess the preliminary criteria for definite RS. Data analysis was based on the statement that Reiter's syndrome consists of an episode of peripheral arthritis of more than 1 month duration occurring in association with urethritis and/or cervicitis. During the initial episode of RS, 70 of the 83 RS patients satisfied the criteria, yielding a sensitivity of 84.3%.