© 2018, Springer Nature Singapore Pte Ltd. Purpose: The purpose of this study was to assess the usefulness of positron emission tomography/computed tomography (PET/CT) in the differential diagnosis of anterior mediastinal tumors. Methods: A total of 94 patients with anterior mediastinal masses or nodules (male, n = 41; female, n = 53; age, 17–84 years) were retrospectively evaluated. All patients were evaluated by PET/CT and the masses or nodules were histologically diagnosed in our institution. Results: Anterior mediastinal masses and nodules were classified into two disease categories: Low (thymic hyperplasia, thymoma, mature teratoma, and MALT lymphoma) and High (thymic carcinoid, thymic cancer, diffuse large B-cell lymphoma, T-cell lymphoblastic lymphoma, Hodgkin’s lymphoma, and malignant germ cell tumors) groups. The sensitivity and specificity of maximum standardized uptake value (SUV max ) 7.5 for the detection of High group were 77% and 100%, respectively. The SUV max distributions of the WHO histological thymoma types and Masaoka stage thymomas extensively overlapped. Masaoka stage III thymomas had significantly higher SUV max than Masaoka stage I thymomas. Regarding the TNM classification, the SUV max of T3 and T1b thymomas was higher than T1a thymoma. Conclusion: Although the SUVmax of each disease overlapped, PET/CT findings provided useful information for the differential diagnosis of anterior mediastinal masses.