Rhabdomyolysis is a life-threatening condition that involves muscle cell destruction. Among its etiologies, severe hypernatremia is a less common cause. We report a teenage girl with congenital central hypoventilation syndrome and hypothalamus dysfunction syndrome who presented with extreme hypernatremia (sodium, 211 mmol/L) with rhabdomyolysis (creatine kinase, 32,850 U/L) and acute renal failure (creatinine, 6.1 mg/dL) following gastroenteritis with 7-kg weight loss. Rhabdomyolysis subsequently led to acute renal failure and hyperkalemia. Acute hemodialysis was initiated on hospital day 3 for hyperkalemia. This resulted in a 13 mmol/L fall in serum sodium in 3 hours despite using a 156 mmol/L sodium bath, but without the development of cerebral edema or neurological defect. This report highlights an unusual cause of rhabdomyolysis in children and the experience of managing such a difficult clinical situation.