Sudden unexpected death in epilepsy refers to sudden death of an individual with a clinical history of epilepsy, in whom a postmortem examination fails to uncover a gross anatomic, toxicologic, or environmental cause of death. Evidence of terminal seizure activity may not be present. One to two percent of natural deaths certified by the medicolegal death investigator are attributed to epilepsy. Detailed microscopic examination of the brain has increasingly afforded the identification of structural changes representative of epileptogenic foci. The authors present 70 cases of death attributed to sudden unexpected death in epilepsy. These cases were classified as follows: individuals who lacked a gross brain lesion, those who had a brain lesion demonstrable at autopsy, and those who lacked neuropathologic evaluation because of decomposition or because only an external examination was done. All of the subjects had a clinical history of seizures. The authors confirm that various microscopic findings, including neuronal clusters, increased perivascular oligodendroglia, gliosis, cystic gliotic lesions, decreased myelin, cerebellar Bergmann's gliosis, and folial atrophy, are present in a higher percentage of the brains of sudden unexpected death in epilepsy subjects than in the brains of age- and sex-matched control subjects.