OBJECTIVE: This study concernes the usefulness of 11C-methyl-L-and D-methionine(Met)-positron emission tomography(PET) for gliomagrading and detection of recurrence in gliomas, compared with fluorine-18, 2-fluoro-deoxyglucose(FDG)-PET. METHODS: Eighty patients underwent Met-PET study for evaluation of glioma: 37 astrocytomas (WHO grade II, 3; III, 8; IV, 26), 27 oligodendrogliomas (WHO grade II, 16; III, 11), and 12 suspicious recurrent gliomas. All images were taken within 2 weeks before operation. For suspicious recurrent cases on magnetic resonance images, both FDG-PET and Met-PET were performed. RESULTS: In astrocytoma, Mean maximum standard uptake value(SUV) of region of interest(ROI) was not different between WHO grades (p=0.108), but ROI/normal contralateral tissue SUV (T/N) ratio was statistically different between WHO grades (p=0.002). T/N ratio was more closely related to visual scale than maximum SUV of ROI (p<0.001 and p=0.107 respectively). In oligodendroglioma, there was no statistical difference between WHO grades in view of maximum SUV and T/N ratio. For recurrent gliomas, sensitivity of FDG-PET and Met-PET was 25% and 100%, while specificity of FDG-PET and Met-PET were 100% and 80%, respectively. CONCLUSION: Met-PET might be an appropriate tool for tumor grading in astrocytom a and be more sensitive for detection of recurrence in gliomas than FDG-PET.