Postural control changes were studied in 27 patients with Parkinson's disease after unilateral posteroventral pallidotomy (PVP). Patients were evaluated before PVP and at 3, 6 and 12 months post-PVP, both 'off' and 'on' parkinsonian medications, with selected evaluation tools representing functional performance, functional balance and posturographic components of balance. The majority of variables in the 'off' state were significantly improved at 3 months post-PVP. Improvement was maintained at 6 months but had declined for some variables by the 12 month follow-up. Standing up from a chair (P = 0.009), the balance and gait sections of the Performance-Oriented Assessment (P < or = 0.0004), and the limits of stability (LOS) posturography variables (P < 0.0005) of the average time to reach a target, the number of targets missed and the initial excursion distance to the target (P = 0.029) retained significant improvement at the 12 month follow-up. When the patients were in the 'on' state, LOS posturography variables of average time to target, average path length deviation, and the number of targets missed were the only variables significantly improved at 3 months post-PVP (P = -0.013) and this improvement was maintained at 12 months post-PVP (P = 0.012-0.041). Unilateral PVP improves axial symptoms of Parkinson's disease involved in functional performance such as gait disturbance as well as improving postural stability in the 'off' state. Generally, the maximum improvement is seen at 3 months post-PVP with many variables remaining significantly improved at 12 months post-PVP. Axial dyskinesias in the 'on' state are also significantly reduced with the improvement maintained at 12 months post-PVP. These findings suggest that unilateral pallidotomy is not only effective in abolishing levodopa-induced dyskinesias, but that it also improves the axial signs of Parkinson's disease.