Most thymomas are diagnosed and staged at the time of surgical intervention. Surgical resection is the preferred treatment of patients who can tolerate surgery and have a mediastinal mass that is suspected of being a thymoma. A total thymectomy with complete resection of all tumor can be achieved in nearly all stage I and stage II patients and in 27% to 44% of stage III patients. Postoperative radiation therapy is generally employed for stage II and stage III patients. Patients with stage IVa disease can only rarely be resected completely and are usually offered debulking surgery and postoperative radiation therapy with or without chemotherapy.