Molecular genetic research in epilepsy is most promising in the homogeneous, genetically determined forms of the disease. The phenotype-genotype strategy used makes some epileptic syndromes more suitable for such study than others. Unequivocal clinical presentation, mendelian transmission with similar clinical expression in close relatives, and sufficiently large numbers of affected families are requisites. This makes idiopathic generalized epilepsies (IGEs), particularly absence and juvenile myoclonic epilepsies (JMEs), suitable subtypes for genetic analysis. Results of family studies to date show that five IGE syndromes have a common genetic origin. Linkage studies have localized a gene defect on chromosome 6p that predisposes to a group of IGEs: JME, absence epilepsy, and generalized tonic-clonic seizures in epilepsy families with JME probands. Environmental and additional genetic factors are other areas requiring further study to elucidate the discriminant factors associated with different varieties of IGE.