Offspring of women with epilepsy who are taking anticonvulsant medications have an increased incidence of clefting abnormalities. However, there is disagreement as to the extent to which this increase is due to a teratogenic effect of anticonvulsant medications or to a familial association of epilepsy and clefting. Some investigators suggested, but were unable to demonstrate adequately, that clefting and epilepsy associate together in families. In order to address this issue, individuals with a clefting disorder and their relatives were ascertained to determine whether clefting and epilepsy aggregate together in families. The incidence of epilepsy was not increased over that in the general population with a standardized morbidity ratio (SMR) for epilepsy of 0.9 (95% CI 0.2-2.6) for first-degree relatives (excluding parents) and 0.0 for second-degree relatives. The SMRs ranged from 0.7-2.2 for the individual relative types (parents 1.5, sibs 0.7, children 2.2) and were also not increased. These results do not support suggestions that clefting and epilepsy segregate together in families.