An 18-year-old mentally normal epileptic boy had frequent left brachiofacial or unilateral motor seizures which started at age 4 years and ceased 10 years later. Seizures were exclusively sleep-related. No relapse followed antiepileptic drug (AED) discontinuation. Left arm slight paresis and left hand astereognosia occurred at age 10 years. Awake EEGs showed persistent right rolandic discharges increased by sleep. Somatosensory evoked potentials (SEPs) were giant with left median nerve stimulation. Computed tomography (CT) and magnetic resonance imaging (MRI) disclosed right opercular macrogyria. We suggest that the structural brain lesion was causally related to his "idiopathic" partial epilepsy. Similar case reports and pathologic studies will elucidate the morphologic substrate of the underlying functional disorder in idiopathic partial epilepsies.