Mendelian forms of benign myoclonic epilepsies where a chromosomal locus has been defined include (1) the autosomal dominant (AD) juvenile myoclonic epilepsy (JME) in chr. 6p11, (2) the autosomal dominant childhood absence epilepsy which evolves to JME in chr. 1p, (3) familial adult myoclonic epilepsy of Yasuda and Inazuki, and (4) possibly JME within the idiopathic generalized epilepsy susceptibility gene in chr. 8 reported by Zara et al (1995). Other myoclonic epilepsy syndromes with onset in the first year of life (Aicardi's Neonatal (Early) Myoclonic Encephalopathy, West's Syndrome, Dravet's Severe Myoclonic Epilepsy, and Dravet's Benign Myoclonic Epilepsy of Infancy), in early childhood (Lennox-Gastaut-Dravet Syndrome, Myoclonic Variant of Lennox Gastaut Dravet Syndrome, Myoclonic-Astatic Epilepsy of Doose, Benign Myoclonic Epilepsies (BME), or even in late childhood (Childhood Absence Epilepsy with myoclonias, vs. Myoclonic Absence Epilepsy) are probably genetically complex diseases. Amongst the progressive myoclonus epilepsy syndromes, specific mutations have already been defined in Unverricht Lundborg disease, ceroid lipofuscinoses 3 or Spielmayer Voight syndrome within Battens disease, sialidosis, dentadorubropallidoluysian atrophy and the mitochondrial syndrome MERRF. Most recently our laboratories established the locus for Lafora's disease in chr. 6q and results are speedily moving towards the definition of its mutation.