A hemispherectomy was performed on a girl of 20 because of progressively uncontrollable seizures and behavioral changes resulting from major head trauma at the age of five. Psychomotor development up to this age had been normal. Today she shows little impairment in higher nervous function depending on the ablated hemisphere. Left-sided motor performance has improved and sensory deficit is scant. There is no hemianopia and the right eye visual field is enlarged. Dichotic listening shows left ear preference and no lesion effect. These findings suggest that significant and positive adaptation may occur in mature brain.