OBJECTIVE The aim of this study was to assess the long-term effects of bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) for Parkinson disease (PD) on sleep, daytime sleepiness, and early morning dystonia and to evaluate the relationship between total sleep time and motor function. METHODS Patients who had undergone bilateral STN DBS and a follow-up evaluation of 6 months (89 patients), 12 months (83 patients), and 24 months (43 patients) were included in this study. The patients were preoperatively assessed using the Unified Parkinson's Disease Rating Scale (UPDRS) in the medication-on and -off conditions, and they completed patient diaries. A subset of patients also completed the Epworth Sleepiness Scale. These assessments were repeated postoperatively with stimulation. The UPDRS activities of daily living (ADL) and motor scores as well as total sleep hours were significantly improved at 6, 12, and 24 months poststimulation and with no medication compared with baseline values. Increased sleep time was significantly correlated with improvements in bradykinesia but not with tremor or rigidity. Patient-reported sleep problems and early morning dystonia were reduced after STN DBS. Antiparkinsonian medications were significantly reduced after STN DBS; however, there were no changes in excessive daytime sleepiness 6, 12, or 24 months after surgery. CONCLUSIONS Bilateral STN DBS increased total sleep time and reduced patient-reported sleep problems and early morning dystonia for up to 24 months posttreatment. These changes in sleep were related to improvements in functioning, specifically those affected by bradykinesia. Despite significant reductions in antiparkinsonian medications, STN DBS did not reduce excessive daytime sleepiness.