Ten patients with movement-induced attacks of choreoathetosis are described. The illness seems to be familial in a significant portion of cases and suggestive of an autonomic recessive mode of inheritance in this and other reports, but dominant patterns have been described. The manifestations and treatment of the syndrome are discussed. The pathophysiology of the illness and its relationship to epilepsy are discussed, and paroxysmal dysfunction of the basal ganglia related to a maturational lag of certain control circuits is postulated. This may result in abnormal oscillations in the "feedback" system of the basal ganglia induced by movement One patient died of an unrelated cause and pathological examination revealed no specific abnormality apart from slight neuronal loss from the locus ceruleus. Literature is reviewed with emphasis on the clinical uniformity of cases previously described with those presented here. Significant differences from Mount and Reback''s original case are emphasized. The unique features facilitate identification of this apparently treatable illness.