In double-blind study, diclofenac sodium (Voltaren®), 50 mg two or three times day, was compared with placebo in 32 patients with pain localized to the temporomandibular joint (TMJ). The patients were allocated into two equally large groups. A visual analog scale was used to estimate the pretreatment degree of pain. The treatment effect was assessed as the frequency of joint and muscle pain and by the patients' own evaluation of improvement. The change in the clinical condition was assessed by tenderness to palpation of the TMJ and masticatory muscles and by mandibular mobility. The frequency of TMJ pain showed greater reduction in the diclofenac group than in the placebo group, and there was significant reduction of daily TMJ pain in the diclofenac group. The diclofenac group also showed significant decrease in tenderness to palpation of the masticatory muscles in comparison with the placebo group. The patients with short duration of pain showed the best response to diclofenac. There was no evidence in this study to prove that diclofenac should be used as primary treatment of TMJ pain, but it could be used as a complement to other treatments of acute TMJ pain.