Our purpose was to measure the change in quality of life (QoL) following deep brain stimulation of the globus pallidus interna (GPi-DBS) in advanced Parkinson's disease (PD), and identifies any associations with changes in motor features of the disease. Eleven patients (age range 54-69 years, 2 women) underwent GPi-DBS (4 unilateral, 7 bilateral). Outcome measures included assessment of PD-specific QoL (mean 8 months postsurgery) using the PDQ-39 questionnaire, and standard motor assessments. Off-period UPDRS III motor scores fell by (43 +/- 8)% (mean +/- SEM). Dyskinesia severity was reduced on the abnormal involuntary movement scale by (80 +/- 3)% and UPDRS IVa by (58 +/- 8)%. QoL as assessed by the PDQ39SI improved by (30 +/- 5)%, with significant improvements in mobility, activities of daily living, bodily discomfort, emotional wellbeing, communication, and cognitions subscales. Bilateral and unilateral groups demonstrated equivalent PDQ39SI improvement. QoL improvement was highly correlated with dyskinesia reduction but not reduction in UPDRS score or age at surgery. GPi-DBS markedly improves QoL in advanced PD. The impacts are broad and improve QoL domains not directly affected by the motor symptoms of the disease. Reduced dyskinesia plays a major role in the improvement of QoL in GPi-DBS treated patients. (C) 2007 Movement Disorder Society.