Asymptomatic rhabdomyolysis of unknown etiology. A 7-year-old boy developed rhabdomyolysis with a peak creatine phosphokinase level of 261,400 IU/L after his appendectomy. These abnormalities occurred following a 2-3-day illness consisting of upper respiratory tract symptoms, fever, and abdominal pain mimicking acute appendicitis. At the time of operation, a normal appendix was removed, and mesenteric lymphadenitis was noted. The myoglobinuria and elevation of creatine phosphokinase were transient, and the patient remained asymptomatic. We review various causes of right lower quadrant pain and rhabdomyolysis and address the roles of malignant hyperthermia and infectious agents. The possible cause of the phenomena observed in this patient is discussed. 