Two patients are reported with hemiballismus due to lesions in the striatum as documented on CT scan. The involuntary movements persisted for one and five years respectively. A third patient with more typical self-limited hemiballismus had no evidence of a causative lesion on CT scan. It is proposed that lesions outside the subthalamic nucleus of Luys may interfere with the compensatory mechanisms which can result in the spontaneous resolution of hemiballistic movements. None of the patients benefited from the use of sodium valproate therapy, however, pimozide reduced the severity of the dyskinesia in the two with longstanding hemiballismus.