Objective: Apathy may be induced by subthalamic nucleus deep brain stimulation (STN-DBS) in Parkinson disease (PD). We therefore wished to test the hypothesis that apathy induced by STNDBS correlates with changes in glucose metabolism, using 18FDG-PET. Methods: Twelve patients with PD were assessed 3 months before (M-3) and 3 months after (M-3) STN-DBS with 18FDG-PET and the Apathy Evaluation Scale. Results: Apathy had significantly worsened at M-3 after STN-DBS. Positive correlations were observed between this variation in apathy scores and changes in glucose metabolism, especially in the right frontal middle gyrus (Brodmann area [BA] 10) and right inferior frontal gyrus (BA 46 and BA 47). Negative correlations between the two were observed in the right posterior cingulate gyrus (BA 31) and left medial frontal lobe (BA 9). Conclusion: These preliminary results confirm the role of the subthalamic nucleus in associative and limbic circuitry in humans and suggest that it is a key basal ganglia structure in motivation circuitry.