The effects of thermal water from Cserkeszölö in Hungary were appraised in a randomised, double blind study conducted on 58 patients with osteoarthritis of the knee. Balneotherapy was delivered as a 15-day course of 30-min daily sessions performed with thermal water (active treatment) or tap water of similar colour and odour (placebo treatment). The musculoskeletal status of participants was evaluated at baseline, at the end of the balneotherapy course, and 3 months later. Study endpoints (initial pain, range of motion, tenderness on palpation, stair climbing, physicians' opinion and subjective rating by patients, and ambulation) were assessed using visual analogue scales and symptom scores. Both groups improved; however, the magnitude of improvement was significantly greater in patients treated with thermal water from Cserkeszölö.