Positron emission tomography (PET) using [18F]fluorodeoxyglucose (FDG) is a useful modality to examine many kinds of tumors, including primary bone tumors. Malignant bone tumors show higher FDG accumulation than benign tumors and earlier reports mention that FDG-PET can differentiate malignancy from benignancy; however, some benign bone tumors present with high FDG accumulation, which increases false positive rates in FDG-PET. FDG accumulation reflects glucose metabolism and thereby FDG-PET can be used for staging malignant bone tumors, which require a large amount of glucose. Combined with conventional studies, such as magnetic resonance imaging (MRI) and scintigraphy, FDG-PET can more accurately decide the staging. Finally, FDG-PET is also applied to evaluate the chemotherapy response of malignant bone tumors and is expected to predict a patient’s prognosis and to help to decide appropriate chemotherapy agents.