In ten patients with parkinsonism a radiosurgical operation with the Gamma Knife was performed in which a small lesion was created in the head of the caudate nucleus bilaterally. Preoperatively, in all cases bradykinesia was the main complaint and in all patients conventional drug treatment no longer resulted in a satisfactory response. After a follow-up period of one month six patients showed clear benefit. There was no complication or side effect that could be related to this form of treatment. Pre- and post-operative testing was performed with the Unified Parkinson Rating Scale and with objective motor tasks. The main improvement seen concerned bradykinesia and rigidity: tremor was ameliorated to a lesser extent. Possible mechanisms underlying the improved motor function are discussed as well as the role of lesioning of the striatum in light of transplantation neurosurgery.