Stereotactic ventroposterolateral pallidotomy in 46 parkinsonian patients resulted in a complete or almost complete and long-lasting relief of rigidity and hypokinesia in 91% of the patients. Good tremor effect was obtained in 80% of them. The L-dopa-induced dyskinesias, gait and speech improved in most patients. Complications were observed in 7 cases after 51 pallidotomies, i.e. 14% (partial homonymous hemianopia in 6 and transient dysphasia and facial weakness in 1). We believe that the good effect of surgery is based on interruption of some striopallidal or subthalamopallidal pathways.