Functional brain imaging using 18F fluorodeoxyglucose (FDG) and positron emission tomography (PET) has greatly enhanced our understanding of brain function both in normal conditions as well as in a wide variety of neuropsychiatric disorders. We review the uses of FDG PET in the diagnosis, management, and follow-up of patients with neuropsychiatric disorders. This article will also explore what FDG-PET imaging has revealed in these neuropsychiatric disorders and how these findings relate to both research and clinical applications.