Thymomas are rare, slow-growing neoplasms that are considered to be malignant because of their potential invasiveness. The most widely used staging system is that of Masaoka and colleagues, which takes into account the extent of clinical and histopathologically determined disease involvement. However, recent data suggest that the staging system of the French Study Group on Thymic Tumors (GETT system), which is based on the surgical and pathologic features of the tumor, may be superior to the Masaoka system. Total resection followed by radiation therapy is the treatment of choice for all thymomas, except stage IA tumors, which can be treated with surgery alone. Chemotherapy can improve the outcome of invasive Masaoka stage III and IV thymomas or recurrent thymomas. Only platinum-containing regimens show consistent efficacy.