In this series of 21 patients with hemiballism-hemichorea we found an identifiable cause in all. Unlike most other studies in which stroke was the most important cause of the movement disorder, in almost half (10 of 21) of our patients some other cause was found. Hemiballism-hemichorea was often the presenting feature of underlying medical disease. Besides the subthalamic nucleus, other subcortical structures may be involved in the pathogenesis of this hemihyperkinesia. While the movement disorder often improves spontaneously or with pharmacologic therapy, the underlying disease may result in serious consequences.