Mediastinum can comprise a wide diversity of malign and benign tumors. Thymus tumors, lymphomas, germ cell tumors, thyroid and parathyroid masses, metastasis, and neurogenic tumors are the common tumors detected in the mediastinum. This review includes the usage of F-18 fluorodeoxyglucose positron emission tomography/computed tomography (CT) in evaluation of mediastinal masses. Also, CT and clinical features of defined masses are briefly presented.