Thirty-one patients (26 males, 5 females) with mean age 35 +/- 19 years (range 8 to 85 years) were diagnosed as non-traumatic rhabdomyolysis by clinical findings and elevation of serum creatine kinase (CK) between January 1989 and December 1993. Causes, laboratory measures, clinical courses, and outcome were reviewed retrospectively. Drug abuse, seizure, and excessive activity are the most common etiologies for non-traumatic rhabdomyolysis. Twelve patients presented with muscular pain and seven patients with muscle weakness. Twenty eight patients had urinalysis and five of them (18%) had negative orthotolidine dipstick test. Only seven patients (25%) were detected positive orthotolidine test without microscopic hematuria. Patients with acute renal failure had higher levels of potassium and uric acid. The patients who developed acute renal failure after admission had significantly higher levels of uric acid. The peak levels of CK did not correlate with development of acute renal failure. There was no episode of hyercalcemia. Seventeen patients (55%) had acute renal failure. Hemodialysis was required in nine cases. All survivors recovered with normal renal function except one who needed maintenance hemodialysis after two months follow-up. Two patients died of multi-organ failure and sepsis.