This article summarizes the clinical applications of positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) as a radiopharmaceutical for the evaluation of various body tumors. FDG-PET is an imaging modality allowing direct evaluation of cellular glucose metabolism, and most malignant cells have increased levels of glucose transporter proteins and glycolytic enzymes. Therefore, applications for FDG include differentiation of malignant tumors from benign lesions, diagnosis, staging, monitoring therapy, and detecting recurrence of tumors that trap FDG. Currently, the biggest use for FDG imaging is nodes and metastases staging of these tumors.