Background. MRI alone has limited accuracy for delineating tumor margins and poorly predicts the aggressiveness of gliomas, especially when tumors do not enhance.This study evaluated simultaneous 3,4-dihydroxy-6-[18F] fluoro-L-phenylalanine (FDOPA)-PET/MRI to define tumor volumes compared to MRI alone more accurately, assessed its role in patient management, and correlated PET findings with histopathology. Methods. Ten patients with known or suspected gliomas underwent standard of care surgical resection and/or stereotactic biopsy. FDOPA-PET/MRI was performed prior to surgery, allowing for precise co-registration of PET, MR, and biopsies.The biopsy sites were modeled as 5-mm spheres, and the local FDOPA uptake at each site was determined. Correlations were performed between measures of tumor histopathology, and static and dynamic PET values: standardized uptake values (SUVs), tumor to brain ratios, metabolic tumor volumes, and tracer kinetics at volumes of interest (VOIs) and biopsy sites. Results. Tumor FDOPA-PET uptake was visualized in 8 patients. In 2 patients, tracer uptake was similar to normal brain reference with no histological findings of malignancy. Eight biopsy sites confirmed for glioma had FDOPA uptake withoutT1 contrast enhancement.The PET parameters were highly correlated only with the cell proliferation marker, Ki-67 (SUVmax: r = 0.985, P =.002). In this study, no statistically significant difference between high-grade and low-grade tumors was demonstrated.The dynamic PET analysis of VOIs and biopsy sites showed decreasing time-activity curves patterns. FDOPA-PET imaging directly influenced patient management. Conclusions. Simultaneous FDOPA-PET/MRI allowed for more accurate visualization and delineation of gliomas, enabling more appropriate patient management and simplified validation of PET findings with histopathology.