Accelerated glycolysis is one of the biochemical characteristics of cancer cells. Based on this fact, positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) has been used in the diagnosis of various cancers. After intravenous injection of FDG and PET scans, most cancers are identified by high FDG accumulation. This metabolic tumor imaging method has been used successfully in the differentiation of benign and malignant tumors, in the diagnosis of metastasis or recurrence, in the detection of primary unknown cancers, and in cancer screening. Because the degree of FDG accumulation reflects tumor glucose consumption, quantification of FDG uptake by PET can be used in predicting biological malignancy and in monitoring treatment in both radiation and chemotherapy. The potential utility of Glut-1 and hexokinase, reported to be responsible for increased glucose metabolism, as biological markers of cancers is yet to be determined.