Neuropathological studies of a woman with chorea-acanthocytosis were reported. The patient clinically showed generalized epileptic seizures, choreatic involuntary movements, hypotonia , areflexia, neurogenic muscular atrophy, tongue-biting and acanthocytosis of the peripheral blood and died from asphyxia at the age of 34. Autopsy revealed atrophy of the caudate nucleus but the cerebral cortex was well preserved. Histological examination showed severe neuronal loss associated with moderate fibrous gliosis of the caudate. The putamen was similarly but less markedly affected. The small striatal neurons were more severely depopulated than the large neurons, although the latter were not spared. Cytometrical study of the caudate head revealed that the remaining small neurons were significantly larger in size than the normal small neurons of the same area. The anatomical substratum of the choreatic involuntary movements in chorea-acanthocytosis is thought to be the degeneration of the striatum, especially the caudate nucleus. Neuropathological differentiation of chorea-acanthocytosis from Huntington's chorea which shows similar pathology was discussed.