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Background 18F-fluorodeoxyglucose (FDG) is the most widely used radiotracer in tumor imaging,but its use for brain gliomas and recurrence is limited by the high 18F-FDG uptake in normal brain tissue.11C-methionine (MET) has low uptake in the normal brain tissue,providing potential advantages over 18F-FDG.The aim of the study was to investigate the diagnostic value of 11C-MET compared to 18F-FDG positron emission tomography and computed tomography (PET/CT) in patients with suspected primary and residual/recurrent gliomas.Methods Eighty paired PET/CT scans using 11C-MET and 18F-FDG were performed on 44 newly diagnosed patients with suspected gliomas and 36 post-operative patients with suspected residual/recurrent tumors.PET/CT results were evaluated by visual and semiquantitative analysis.The sensitivity,specificity and accuracy for detection of gliomas and residual/recurrent tumors were calculated using visual analysis.Tumor to contralateral normal gray matter (T/G) ratio was calculated for semiquantitative analysis.Results Final pathology of the 44 newly diagnosed patients included 26 gliomas (14 high-grade and 12 low-grade tumors) and 18 non-glioma benign lesions.Residual/recurrent gliomas were verified in 28 patients and excluded in 8/36 post-operative patients by subsequent histopathologic examination and/or clinical follow-up for more than six months.The sensitivity,specificity and accuracy of 11C-MET PET/CT were 88.5％,83.3％ and 86.4％ for gliomas and 96.4％,87.5％ and 94.4％ for residual/recurrent gliomas,respectively.The sensitivity,specificity and accuracy of 18F-FDG PET/CT were 50.0％,88.9％ and 65.9％ for gliomas and 46.4％,100.0％ and 58.3％ for residual/recurrent gliomas,respectively.11C-MET had a higher sensitivity than 18F-FDG (83.3％ vs.33.3％,P=0.031) in low-grade gliomas,but had no significant difference in sensitivity from 18F-FDG for high-grade gliomas (92.9％ vs.64.3％,P=0.219).11C-MET T/G uptake ratios in high-grade gliomas,low-grade gliomas and benign lesions were 1.94±0.53,1.78±0.61 and 1.06±0.34,respectively.18F-FDG T/G uptake ratios in high-grade gliomas,low-grade gliomas and benign lesions were 1.05±0.37,0.66±0.14 and 0.63±0.17,respectively.Conclusions 11C-MET PET/CT is superior to 18F-FDG PET/CT in detecting and delineating gliomas and residual/recurrent tumors,especially low-grade gliomas and residual/recurrent lesions present in gray matter,but its role in non-invasive grading of the tumors is limited.