OBJECTIVE To assess the efficacy and safety of sulphasalazine in reactive arthritis. METHODS Double blind placebo controlled trial of six months duration comparing sulphasalazine 2-3 g per day (n = 37) with matching placebo (n = 42) in adults with active reactive arthritis (age 19-57 years, median 34). Treatment response was evaluated once a month by changes in erythrocyte sedimentation rate (ESR), pain, peripheral arthritis, tender iliosacral joints, entesopathy, extra-articular manifestations, and working ability. RESULTS 15 patients in the sulphasalazine group and eight in the placebo group withdrew from the study prematurely. Adverse events, primarily gastrointestinal, were the main reason for withdrawal in the actively treated group. Intention-to-treat analyses showed significant improvements over time in both groups in ESR, pain, and number of swollen joints (P < 0.01). Number of days on sick leave decreased significantly in the sulphasalazine group only (P < 0.01). No significant differences between the two groups were present after six months. Among the patients completing the trial according to protocol, persistent complete remission had occurred within two months in five (23%) of the actively treated, but in no placebo treated patients (P = 0.013). CONCLUSIONS Sulphasalazine seemed to improve only the very short term outcome of reactive arthritis. The possible beneficial effect of the drug should also be weighed against the risk of adverse events. Although these were mainly mild, almost 25% of the patients in the actively treated group gave up treatment for this reason.