A case is described in which, after administration of diclofenac for 13 days for arthritis attributed to gout, the patient experienced erythema multiforme followed by muscle weakness, elevation of serum creatine phosphokinase (CPK) level from 101 to 83,770 U/L, 100% muscle isoenzyme, blood urea nitrogen (BUN) level from 15 to 87 mg/dL, creatinine level from 1.0 to 2.1 mg/dL and urine myoglobin level to 1,190 micrograms/dL (N < 1.2). The diagnosis was rhabdomyolysis due to diclofenac, with myoglobinuria resulting in mild renal failure. Treatment consisted of discontinuing diclofenac and administering sufficient fluids to prevent progression of myoglobinuric renal failure. Serum CPK level gradually returned to normal by day 50, BUN and creatinine levels by day 28, and muscle strength between day 90 and 180. Rhabdomyolysis due to diclofenac or to other nonsteroidal antiinflammatory drugs has not been reported.