Spa therapy is frequently used in daily rheumatological practice, but its benefit remains to be evaluated. A prospective randomized controlled study was conducted in 1993 in patients with osteoarthritis of the hip, knee or lumbar spine. Treatment was either spa therapy at Vichy (France) of 3 weeks duration (spa group) or usual therapy (control group). Assessment criteria were pain (visual analogue scale), functional impairment (Lequesne's index for hip or knee disease, Main and Waddell's for lumbar spinal diseases), quality of life index [revised Arthritis Impact Measurement Scale (AIMS2)], and analgesic and/or non-steroidal anti-inflammatory drug (NSAID) consumption. Patients were included by randomization into one of the two arms (spa or control) and assessment criteria were collected before spa therapy or the control period, and 3 and 24 weeks thereafter. A total of 188 patients (lumbar spine 95, knee 64, hip 29) were included in the study (spa group 91, control group 97). Changes in the assessment criteria after a 6 month follow-up period showed improvement in terms of pain, functional impairment and quality of life, with a reduced intake of symptomatic drugs (NSAID and analgesic drugs) in the spa group. This study suggests that spa therapy of 3 weeks duration has a prolonged, beneficial, symptomatic effect in osteoarthritis.