Myopathy is a well-recognized complication of persistent hypokalemia. Although hypokalemic myopathy may be due to divers diseases or to drug administration, hypokalemic rhabdomyolysis as a complication of under-treated 11-hydroxylase deficiency has not previously been described in the literature. We describe a 10-year-old boy with under-treated 11-hydroxylase deficiency who developed rhabdomyolysis following severe hypokalemia. Patients with under-treated 11-hydroxylase deficiency may present with hypokalemia in association with muscle weakness; if serum potassium is markedly low, rhabdomyolysis may occur. Hypokalemia-induced rhabdomyolysis should be carefully followed.