The offspring of mothers with epilepsy are considered to be at developmental risk during pregnancy from: (1) generalized maternal seizures (hypoxia); (2) teratogenicity of antiepileptic drugs (AEDs); and (3) adverse socio-familial conditions associated with having a chronically sick mother. Sixty-seven children of mothers with epilepsy and 49 children from non-affected mothers, matched for control variables, were followed from birth to adolescence (53 males, 63 females; mean age 14y 2mo, range 10-20y). Prediction of intellectual performance of these children during adolescence was calculated from the following variables: maternal generalized seizures, prenatal exposure to AEDs, and quality of family stimulation (HOME Inventory) assessed in children at 2 years of age. Children who were prenatally exposed to AEDs achieved lower IQs than control children at adolescence. This effect was moderately significant for children who had been exposed to monotherapy (6 IQ points lower), but was considerable in those exposed to polytherapy (12 IQ points lower). Generalized seizures during pregnancy, observed in half the mothers, did not exacerbate this effect. Relative to prenatal risk status, the quality of the family environment had varied effects on intellectual development. Children with prenatal risks appeared to be more vulnerable to environmental disadvantage than control children, but they also showed longer-lasting effects of environmental support.