An overemphasis on molecular genetic advances in epilepsy is in danger of missing the major contribution that clinical genetic studies make in predicting the likely benefit of molecular research efforts. Genetic epidemiology, twin, and family studies suggest that some individual epilepsy genes raise the risk for developing many different types of epilepsy but that specific combinations of these genes determine specific epilepsy phenotypes. Experimental data show how differences in drug response can result from inherited differences in drug sensitivity and there is emerging data on the genetic basis of harmful adverse drug reactions and teratogenesis. These developments predict a future in which epilepsy is ultimately classified on the basis of its oligogenic architecture, effective treatments are tailored to the appropriate patient and harmful adverse drug reactions avoided in those who are sensitive.