In a double-blind, placebo-controlled comparative study in 60 patients with ankle sprains suffering from moderate to severe inflammation and tenderness, the efficacy and tolerability of 150 mg/day diclofenac potassium given for 7 days was superior to that of 1.2 g/day ibuprofen which was, in turn, superior to placebo. Efficacy was assessed by volumetric evaluation of inflammation of the injured ankle, tenderness on finger pressure, pain on movement and the severity of the joint injury. Patients used visual analogue scales to assess severity of pain at rest and on walking before and during treatment. Diclofenac potassium was significantly superior (P less than 0.02) to ibuprofen for all measures of efficacy (except severity of joint injury) and ibuprofen was consistently superior to placebo. No serious adverse effects were reported. In conclusion, diclofenac potassium has been demonstrated to be effective in the treatment of acute ankle sprains and it had a rapid onset of action and good tolerability.