Idiopathic epilepsies are mainly due to genetic factors. In most cases the mode of inheritance is either oligogenic or multifactorial. Only a few rare idiopathic epilepsies are single gene disorders. Monogenic epilepsies offer the chance to identify genes/gene families which might also be involved in the aetiology of common forms of the disease. The genetic basis of two monogenic epilepsies have recently been identified: autosomal dominant nocturnal frontal lobe epilepsy and benign familial neonatal convulsions.