Seventeen pediatric patients with posterior fossa brain tumors were studied with 2-[18F]fluoro-2-deoxy-D-glucose (FDG) and positron emission tomography (PET). The FDG uptake was ranked by two observers, and the results were correlated with tumor histology. Increased FDG uptake was associated with more malignant and aggressive tumor types. Heterogeneity of FDG uptake was associated with previous therapy, including radiation therapy and chemotherapy. 2-[18F]Fluoro-2-deoxy-D-glucose PET will likely be an important adjunct in the management of pediatric posterior fossa tumors, much as in adult patients with brain tumors. © 1992 Raven Press, Ltd., New York.