OBJECTIVE: Selective impairment of executive function has been shown in Parkinson's Disease (PD) patients undergoing Deep Brain Stimulation (DBS) of the Subthalamic Nucleus (STN). However, some patients experience difficulties in daily life, such as dissension in interpersonal relationships or a loss of lifestyle balance, in the short term after surgery. Our hypothesis is that these difficulties might be related to executive dysfunction. To elucidate the involvement of executive dysfunction in these difficulties, we assessed motor and executive function in the short term and long term after surgery. METHODS: We examined motor function and executive function in 30 patients who underwent bilateral STN-DBS for medically refractory PD. Patients were evaluated for executive function 1 month before surgery, 1 month after surgery, and 12 months after surgery using the Trail Making Test (TMT), the Modified Stroop Color Word Interference Test (MST) and tests of Verbal Fluency (VF). RESULTS: TMT-B, TMT (B/A), MST-B, VF-phonemic and VF-semantic scores were significantly poorer 1 month after STN-DBS. TMT-B, TMT (B/A) and VF-phonemic recovered to preoperative levels by 12 months after surgery. A reduction in dopaminergic medication 1 month after surgery was significantly correlated with deterioration of TMT (B/A). CONCLUSION: Temporary deterioration of executive function may occur in the short term after STN-DBS, whereas motor function is usually improved. PD patients undergoing STN-DBS should be managed during this period to better predict temporary executive dysfunction. Excessive reduction of dopaminergic medication after surgery might, at least in part, result in this deterioration of executive function.