Idiopathic epilepsies account for approximately 40% of all epileptic diseases. For a long time, it has been known that genetic factors play a major role in the etiology of these diseases. Although oligogenic or polygenic inheritance is suspected in most of the common syndromes, a few rare idiopathic epilepsies are single-gene disorders. They offer a chance to identify candidate genes that also may be involved in epilepsies with complex inheritance. In recent years, major progress has been made regarding the analysis of genetic factors in idiopathic epilepsy. For the first time, gene defects could be linked to two idiopathic epilepsies. Mutations in the CHRNA4 gene, which codes for the alpha4 subunit of the neuronal nicotinic acetylcholine receptor, lead to autosomal dominant nocturnal frontal lobe epilepsy, a rare idiopathic partial epilepsy syndrome. Two highly homologous voltage-gated potassium channels, KCNQ2 and KCNQ3, were found to be mutated in benign familial neonatal convulsions.