Ventroposterolateral pallidotomy was used in the surgical treatment of 259 patients suffering from intractable Parkinson's disease. Pallidotomy was equally effective against tremor, rigor, bradykinesia, and the L-dopa-induced dyskinesias. The effect of surgery seemed to be long-lasting, and side effects were rare. The author believes that the beneficial effect of pallidotomy is based on interruption of striopallidal and pallidosubthalamic pathways.