Single gene disorders offer the best opportunity for identification of genetic linkage and of abnormal genes. Epilepsies with single gene inheritance include symptomatic epilepsies where there is associated diffuse brain dysfunction, and idiopathic epilepsies where seizures are the major neurological abnormality. There are over 200 single gene symptomatic epilepsies; most are rare. Gene identification has been achieved in a number of these conditions but these important advances have not yet led to a better understanding of epileptogenesis, because of the associated brain disease. Idiopathic single gene epilepsies include benign familial neonatal convulsions, where genetic linkage to chromosomes 20q and 8q has been found in different families, and benign familial infantile convulsions where linkage is presently unknown. Recently, four autosomal dominant partial epilepsies have been described. In autosomal dominant nocturnal frontal lobe epilepsy a genetic defect in the alpha 4 subunit of the nicotinic acetylcholine receptor was found in one family. This is the first genetic defect described in an idiopathic epilepsy. The other three syndromes are autosomal dominant partial epilepsy with variable foci, autosomal dominant rolandic epilepsy with speech dyspraxia, and familial temporal lobe epilepsy. In the latter condition, linkage to chromosome 10q has been reported in one family, but the genetic defect is unknown. It is likely that other idiopathic single gene epilepsies will be identified. Molecular genetic study of these disorders is likely to lead to discovery of other epilepsy genes. This will lead to an improved understanding of human epileptogenesis with implications for clinical diagnosis, genetic counselling, pharmacological therapy and possibly prevention of epilepsy.