Objective: To investigate the effects of pallidotomy on postural reactions and other motor parkinsonian deficits. Design: Comparison of performance by patients before and after pallidotomy on tests of balance and function. Setting: A Parkinson disease Center of Excellence and Center for Human Performance Testing at a university hospital and research center. Participants: Twenty-nine patients with Parkinson disease undergoing pallidotomy. Main Outcome Measures: Performance results on the United Parkinson's Disease Rating Scale (UPDRS), activities of daily living and motor subscales (parts II and III), and posturography (sensory organization test), which were collected before and 3 and 6 months after surgery with patients in the practically defined off state (medication withheld for at least 12 hours). Results: Data were analyzed with a paired Wilcoxon and Spearman correlation. There was a significant improvement in mean ±SD UPDRS motor subscale score after pallidotomy (before surgery, 52.43 ± 13.46; after surgery, 43.93 ±15.15; z = 3.63; P= .003). There were no significant changes in the UPDRS activities of daily living subscale or average stability scores when the group was examined as a whole. However, examination of individual data revealed that 9 (56%) of 16 patients who could stand independently before surgery showed improvement in either the number of falls or the average stability score. No patient who was unable to stand independently before surgery was able to stand independently after it. Conclusion: Pallidotomy helped improve overall motor function in patients with parkinsonism and, for some patients, also improved postural stability.