Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been reported to have a positive effect on sleep-wake disturbance in Parkinson's disease (PD). We aimed to investigate the long-term effects of STN DBS on sleep in patients with PD. Sixty-one patients with PD who had undergone bilateral STN DBS were followed for 3 years with assessments including the Parkinson's disease sleep scale (PDSS), Epworth sleepiness scale (ESS), total sleep hours per day, Unified PD Rating Scale part I-III, Hoehn & Yahr stage, levodopa equivalent dose, quality of life measure, and depression scale measured preoperatively and at 6 months after postoperatively, and annually thereafter. Among the 61 patients at baseline, 46 patients completed the last follow-up assessment. The total PDSS score significantly improved after STN DBS from baseline up to 3 years after STN DBS (79.0±30, 100.0±23.3, 98.8±23.0, 97.1±29.6, and 93.3±28.0 at baseline, 6, 12, 24, and 36 months, respectively, p = 0.006 for the change over time). Among the eight PDSS domains, the domains for overall quality of a night's sleep, sleep onset and maintenance insomnia, and nocturnal motor symptoms showed significant improvement after STN DBS (p = 0.036, 0.029, and < 0.001, respectively, for the change over time). The total sleep hours per day were increased, but the total ESS score did not show significant change after STN DBS (p = 0.001 and 0.055, respectively, for the change over time). Changes in the total PDSS were associated with changes in the depression and motivation items in the Unified PD Rating Scale part I, depression scale, and quality of life measure, but those variables at baseline were not predictive of changes in the total PDSS after STN DBS. In the largest systematic long-term follow-up study, the improvement in subjective sleep quality after bilateral STN DBS was sustained in PD patients. Improved nocturnal sleep and nocturnal motor symptoms were correlated with an improved mood and quality of life. However, STN DBS did not reduce excessive daytime sleepiness despite reductions in antiparkinsonian medications.