Multiple different types of anterior mediastinal masses may be encountered on computed tomography (CT) imaging, and many of these lesions are neoplastic in etiology. These include masses arising from the thymus, thyroid and parathyroid glands, as well as lymph nodes, pericardium, and vessels and nerves. Often, the CT attenuation of the mass can be helpful in narrowing down the differential diagnosis, and attenuation values suggesting fat, water or calcium may suggest certain diagnoses; significant enhancement of the mass with intravenous contrast may also be a helpful feature. Lesions with fatty attenuation include teratomas, thymolipomas and Morgagni hernias. Lesions that may manifest the attenuation of water include pericardial and thymic cysts, abscesses, and lymphangiomas, as well as neurogenic and germ cell tumors. Multiple types of lesions may contain calcium, including thyroid goiters and cancers, thymomas, thymic carcinomas and carcinoids, treated lymphoma, germ cell tumors, parathyroid adenomas, and lymph nodes involved with silicosis, sarcoid, tuberculosis, fungal diseases and pneumocystis. Contrast enhancement may be seen in lesions of vascular origin and in vascular neoplasms, such as parathyroid adenomas and Castleman's disease. In addition to CT attenuation values, the exact location and morphology of the mass in question, in conjunction with clinical features such as patient age, gender, signs, symptoms, and laboratory values, can usually lead to a short list of possible etiologies, thereby directing appropriate additional diagnostic procedures or therapeutic approaches.