Autosomal recessively inherited progressive myoclonus epilepsies (PMEs) include Lafora disease, Unverricht-Lundborg disease, the neuronal ceroid lipofuscinoses, type I sialidosis (cherry-red spot myoclonus), action myoclonus-renal failure syndrome, and type III Gaucher disease. Almost all the autosomal recessively inherited PMEs are lysosomal diseases, with the exception of Lafora disease in which neither the accumulating material nor the gene products are in lysosomes. Progress in identifying the causative defects of PME is near-complete. Much work lies ahead to resolve the pathobiology and neurophysiology of this group of devastating disorders.