The epilepsies comprise a group of syndromes that are divided into generalized and partial (focal) types. Familial occurrence has long been recognized but progress in mapping epilepsy genes has been slow except for rare cases where the inheritance is easily determined from classical genetic studies. Linkage is established for three generalized syndromes: the EBN1 and EBN2 genes for benign familial neonatal convulsions (BFNC) map to chromosomes 20q and 8q (refs 2-5), the EPM1 gene for Unverricht-Lundborg disease maps to 21q (ref. 6) and the gene for the northern epilepsy syndrome maps to 8p (ref. 7). A claim for linkage of the EJM1 gene for the common generalized syndrome of juvenile myoclonic epilepsy to 6p is currently in dispute. Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) was recently described in five families. We now report the chromosomal assignment, to 20q13.2, for the gene for ADNFLE in one large Australian kindred with 27 affected individuals spanning six generations.