The past decade has seen the identification of many clinical settings in the treatment of primary brain tumors in which information from fluorodeoxyglucose positron emission tomography (FDG-PET) might be useful, if not essential, to therapeutic formulation. FDG-PET is currently used at referral centers in the management of primary brain tumors. The clinical pattern of FDG-PET use was assessed and its value compared to other information sources in clinical decision making. The clinical records of 75 glioma patients who were evaluated by FDG-PET were reviewed. The range of circumstances in which FDG-PET was employed included: pretherapeutic baseline studies for monitoring the effect of a therapy (1% of all cases), mapping of hypermetabolic regions before surgery or biopsy (2%), mapping of hypermetabolic regions before radiotherapy (2%), postsurgical evaluation for residual tumor (2%), assessment of the malignancy of a mass as a substitute for biopsy (11%), and distinguishing between radiation necrosis and recurrent tumor (87%). Other sources of information that contributed to the therapeutic management of patients included: gadolinium-enhanced MRI, contrast-CT, and clinical findings.