From the conditions generically classified as amaurotic familial idiocy, two distinctly different groups have emerged. One is characterized by grossly abnormal profiles for cerebral sphingolipids and consists of GM1-gangliosidosis and GM2-gangliosidosis or Tay-Sachs disease. The other group is composed of cases with normal sphingolipid profiles, but with neuronal accumulation of lipopigments of the ceroid/lipofuscin type, designated as neuronal ceroid-lipofuscinosis (NCL) or Batten's disease. Clinical data on 26 patients with this disorder reveal the course and symptomatology to be variable, but pathomorphologic and biochemical findings are reasonably constant. The course of the disorder is directly influenced by the presence or absence of intractable seizures.