Topographic comparative study of magnetic resonance imaging and electroencephalography in 34 children with tuberous sclerosis. A series of 34 children with confirmed tuberous sclerosis (TS) were studied prospectively by both EEG and magnetic resonance imaging (MRI) at ages ranging from 5 months to 18 years. Size and topography of the cortical tubers were analyzed on axial and coronal views, in T2 sequences, and the large tubers greater than 10 mm were studied. In addition, EEG follow-up data were reviewed retrospectively. Twenty-six patients (76%) had both MRI large cortical tubers and EEG foci, 3 had normal EEG, 2 had normal MRI, and the remaining 3 had only small tubers. The number of large tubers was significantly related to EEG foci. A topographic MRI/EEG correspondence was observed for at least one tuber in 25 of the 26 patients, and correspondence was complete in 10 patients. Large cortical tubers without corresponding EEG foci were observed in 11 patients; these tubers mainly involved the frontal regions and were found before the patients were 2 years old. EEG foci without corresponding tubers were observed in 4 patients. In addition, secondary bilateral synchrony was preferentially observed in patients with frontal lesions and after the age of 2 years. These data confirm that the cortical tubers are epileptogenic and that their expression may be influenced by regional cortical maturation. 