While bilateral stimulation of the subthalamic nucleus (STN) has been commonly applied for patients with advanced Parkinson's disease (PD), surgery in the earlier stage of the disease may yield a better prognosis. We retrospectively analyzed the pre- and postoperative activities of daily living (ADL) of 38 PD patients who had undergone bilateral STN stimulation 3 months earlier. Preoperative Unified Parkinson's Disease Rating Scale (UPDRS) scores for neuropsychiatric, axial and ADL impairments were negatively correlated with the postoperative Schwab & England ADL (S-E) scale in the off-medication status (p < 0.01). Patients with longer disease duration had a lower postoperative S-E scale, but their correlation was not statistically significant (p = 0.0467). Age was not a significant predictor of postoperative ADL. Patients with a preoperative on-medication S-E scale <or=60% (n=14) manifested a greater response rate to surgery than did those with a preoperative S-E scale >or=70% (n=24). However, patients with poorer preoperative ADL were unable to perform ADL independently after surgery (postoperative S-E was 70.0 +/- 12.4% in the on-, and 65.7 +/- 16.0% in the off-medication status) and the difference from patients with better preoperative S-E was significant (postoperative S-E 92.5 +/- 5.3% in the on-, and 90.4 +/- 6.2% in the off-medication status) (p < 0.0001). Our findings suggest that the delivery of STN stimulation earlier in the course of PD may result in greater independence in postoperative ADL.