A 40 year old woman undergoing treatment for cancer of the breast presented with metastatic hemiballism. Diagnosis was supported by the presence of bone and liver metastases and by CT-scan showing an enhanced rapidly growing lesion in the subthalamic region contralateral to hemiballism. Treatment by corticotherapy and neuroleptics was ineffective. Radiotherapy was unsuccessful. Metastatic hemiballism is a rare disease with no effective treatment.