Hemimegalencephaly is a rare congenital brain malformation, usually associated with mental retardation, * refractory epilepsy, and progressive neurological deficits. We report the case of a 19-year-old female with de novo diagnosis of right hemimegalencephaly, normal intellectual function, and history of non-refractory epilepsy. She presented with weakness and paraesthesia of the left leg. Extensive evaluation was negative for other causes for the weakness, which was attributed to progressive neurological damage secondary to long-standing subclinical epileptic activity in the hemimegalencephalic hemisphere. This patient underwent a cerebral fluorodeoxyglucose positron emission tomography that demonstrated near-normal cortical metabolism. Formal neuropsychological evaluation revealed mild deficits in the affected hemisphere, but preserved general intellectual function. This case illustrates the wide phenotypic variations in this condition and raises questions about prenatal counselling for hemimegalencephaly.