Sixty-seven patients with thymoma were surgically treated during the past 19 years in our department. The 5-year, 10-year and 15-year survival rates of total cases with thymomas were 69.2%, 59.6% and 59.6%, respectively. Survival rates of thymoma with MG and without MG were not significantly different. According to clinical stages in Masaoka's classification, there were significant difference between Stage I and Stag III (p < 0.05), Stage I and Stage IV a (p < 0.01), and Stage I and Stage IV b (p < 0.01). We can conclude that complete resection of thymomas lead to better prognosis, and immunochemotherapy using cyclophosphamide, vincristine and OK-432 are effective.