A prospective double-blind, placebo-controlled, randomized study of 24 weeks duration was carried out comparing the efficacy and tolerability of sulphasalazine (SSZ) versus placebo in patients with psoriatic arthritis. A total of 120 patients were included in nine centres. All patients had active disease and fulfilled the criteria of definite psoriatic arthritis of at least 3 months duration. They received either SSZ (2.0 g/day) or placebo. Efficacy variables included pain, patient's overall assessment of joint and skin improvement, morning stiffness, Ritchie articular index, ESR and CRP. An intention-to-treat (ITT) analysis was performed for the 117 patients who qualified (three patients did not qualify due to missing data after baseline). A per-protocol analysis was performed for the 81 patients who completed the 6 months study period (SSZ = 38, placebo = 43). Major reasons for withdrawal were inadequate response (SSZ = 4, placebo = 7) and adverse events (SSZ = 8, placebo = 12). Pain was the only statistically significantly different primary outcome variable at end point in favour of SSZ in the ITT analysis. No significant differences were present in other clinical or biological variables, although there was a trend in favour of SSZ for some variables. SSZ, at a dose of 2.0 g/day, appeared to be a safe treatment in patients with psoriatic arthritis. At this dosage, its efficacy was only demonstrated for the pain variable.