The relationship of febrile seizures to later intellectual and academic performance was examined in a sibling-control study. Amont 431 sibling pairs tested at the age of 7 years, the mean full scale IQ on the Vechsler Intelligence Scales for Children was not different for children who had febrile seizures as compared with siblings who were seizure-free. Neither recurrent seizures nor those lasting 30 minutes or longer were associated with IQ deficit. Poor academic achievement, defined as Wide Range Achievement Test performance more than one grade level below school placement in children with IQs of 90 or above, was equally frequent in index cases and control patients. Febrile seizures were not associated with a decrement in IQ or early academic performance, as judged by comparison of affected children with their siblings.