OBJECTIVE: The study was designed to elucidate regional brain metabolic changes according to a treatment and their relationship with neuropsychological performance changes in obsessive-compulsive disorder (OCD). METHOD: Cerebral glucose metabolic rates were repeatedly measured before and after treatment in 10 patients with OCD using [18F]-2-fluoro-deoxyglucose positron emission tomography (PET). They were compared on a voxel-basis, and the correlations were counted between the regional metabolic changes and the degree to improvement on the neuropsychological assessments. RESULTS: After treatment, the patients showed significant (P < 0.005, two-tailed) regional metabolic changes in multiple brain areas involving frontal-subcortical circuits and parietal-cerebellar networks. Especially, the metabolic changes of the putamen, the cerebellum, and the hippocampus were significantly correlated with the improvement of the immediate- and delayed-recall scores of the Rey-Osterrieth Complex Figure Test (RCFT). CONCLUSION: These results suggest a possibility that metabolic changes of frontal-subcortical and parietal-cerebellar circuit changes may underlie cognitive improvements in patients with OCD.