An 11-month-old male presented with acute gastroenteritis, seizures, and altered mental status. Laboratory workup revealed serum sodium of 177 mmol/L. Magnetic resonance imaging of the brain showed reduced diffusion in the supratentorial white matter, T2 hyperintensities in the left central pons and midbrain, subacute stroke in the right occipital lobe, and bilateral cerebellar hemorrhagic infarcts. The child was presumed to have hypernatremia-induced central pontine and extrapontine myelinolysis. He received 5 days of high-dose methylprednisolone for persistent encephalopathy and spastic quadriparesis with rapid recovery of his cognitive function and neurological examination. The child remained seizure-free and achieved normal development at 3-month and 2-year follow-ups. Osmotic demyelination of infancy may leave children with a significant neurological deficit. For favorable neurological outcome, early steroids should be considered.