A large kindred, with two brothers coming to autopsy, of a syndrome consisting of ataxia, dementia, and some Parkinsonian features is reported; inheritance appears to be autosomal dominant. Neuropathologically, there were plaques and neurofibrillary tangles in the cerebral cortex as well as some in the basal ganglia, particularly reminiscent of the plaques seen in Kuru; there was only minimal spinal cord disease (pyramidal tract field). The problems of classifying this condition — Alzheimer's disease with cerebellar involvement or other entities, such as the Gerstmann-Sträussler-Scheinker condition (1936), especially now that transmission to animals in the latter has been reported — are discussed. Some relevant theoretical considerations derived from animal work, particulary in scrapie, are also reviewed.