To analyze the results, efficacy and safety of unilateral microelectrode guided pallidotomy for the treatment of advanced Parkinson's disease, three months and one year after surgery.23 patients with advanced Parkinson's disease (mean age 58.9 years and mean disease duration 14.4 years) were submitted to pallidotomy. Neurological evaluation, three months (n = 23) and one year (n = 16) after surgery, was performed during the morning in overnight "off" condition and after receiving 100-150% of their usual l-dopa dose. Parkinsonian symptoms were evaluated in each follow up visit through motor scales, activities of daily living scales, a dyskinesia rating scale and motor timed tests.Contralateral dyskinesias improved 92% three months after surgery and 89% at one year. Parkinsonian motor scores were reduced by 36.5% after three months and by 26.7% one year after surgery. In the one year follow up visit, contralateral tremor improved 48%, rigidity 36.2% and bradykinesia 37.4%. All these changes were statistically significant (p0.01). Adverse effects were minor or transient. Antiparkinsonian medication dosage did not significantly change during the study period.Microelectrode guided unilateral pallidotomy is an effective and safe procedure to improve contralateral motor symptoms in Parkinson's disease, being specially useful for the treatment of l-dopa induced dyskinesias.