A prospective intraindividual study of WISC-R testing in the 45 children with epilepsy revealed that: 1) antiepileptic drugs, phenobarbital in particular, resulted in a detrimental effect on the WISC-R scores, 2) of the WISC-R subtests, vocabulary tasks of the verbal test were the most susceptible indicators in children whose FSIQ scores either improved or deteriorated, and 3) in children whose antiepileptic drug dosage remained unchanged while the seizure frequency remained unchanged, both the VIQ and PIQ scores decreased. It was evident that either recurrent seizures or inappropriate medication may exert a detrimental effect on intelligence as expressed by the WISC-R testing. In addition, the possibility that the underlying cerebral pathology associated with the etiology of epilepsy may play a role in a progressive intellectual deterioration was suggested.