We report a case with hemimegalencephaly and catastrophic epilepsy treated early at 4 months by functional hemispherectomy. The boy had intractable continuous epilepsy, with seizures every 10 min, hemiparesis and absence of psychomotor acquisition. Three years after hemispherectomy, the boy is seizure free and has a mild psychomotor delay. Hemiparesis and hemianopsia are unchanged. Early hemispherectomy, before 6 months of age, may control severe epilepsy and preserve the development of higher cortical functions in the nonhemimegalencephalic hemisphere.