Ongoing adverse events (AEs) at 4-years postsurgery in 69 patients with advanced Parkinson's disease (PD) who received deep brain stimulation (DBS) of the subthalamic nucleus (STN) (n = 49) or the internal globus pallidus (GPi) (n = 20), in the framework of a subset of eight centers of a multicenter study, were analyzed by an independent ad hoc committee. At baseline, the patients' age, sex, disease duration, and clinical condition were virtually identical, as was the duration of follow-up. There were 64 AEs reported in 53% of STN DBS patients and eight AEs reported in 35% of GPi DBS patients. Most of the AEs were not deemed severe and were reported to be present "both with and without stimulation." The majority of the AEs affected patients' cognitive, psychiatric and behavioral status, as well as speech, gait, and balance, and most of these AEs occurred in STN DBS patients. When comparing patients who exhibited AEs with those who did not, it was found that in the STN DBS group, the patients with AEs had a longer disease duration, as well as more gait disorders and psychiatric disturbances at baseline.