One hundred thirty subjects with autism in childhood (males 104, females 26) and first seen from 1 to 14 years of age (median 4 years) were followed over 10 years, at Yokohama Central Area Habilitation Center for Children, Japan. Thirty three (25%) developed epilepsy by age 21 years (onset at median age of 14, range 8-26), A lower cognitive level, lower social maturity score, and higher frequency of psychotropic medications were observed in patients with epilepsy vs those without. Febrile seizures occurred in the 2 groups (18% vs 12%). Epileptiform EEGs were recorded in 73% of the epilepsy group vs 21% of non-epilepsy (p<0.001). EEG abnormalities occurred before the onset of epilepsy in 68% of the epilepsy group. Seizures ranged in frequency from 1 to 74 (median 3); 33% had only 1 seizure.