A 9-year-old girl was admitted for the treatment of hyper-natremic dehydration. Her history was significant for psychogenic polydipsia, hyponatremia, and a renal concentrating defect. She presented with a 2-day history of altered mental status, ataxia, lethargy, fever, nausea, vomiting, and diarrhea. Meningitis was ruled out. Over the course of her illness, slow rehydration was maintained with a gradual decrease (10 mEq per 24 hours) of the serum sodium. Despite this care, she developed quadriparesis, and magnetic resonance imaging performed on day 6 of her illness was consistent with osmotic demyelination (central pontine myelinolysis). To rule out an excessively rapid correction of hypernatremia as the etiology of the problem, a myelin basic protein was measured in the cerebrospinal fluid that had been obtained on hospital day 1. The myelin basic protein was 649.50 ng/mL (normal, 0.07-4.10 ng/mL). The current literature is presented regarding the postulated pathogenesis of central pontine myelinolysis and suggested therapies, previous reports of central pontine myelinolysis in children are reviewed, and the potential role of myelin basic protein in its diagnosis is discussed.