The clinical features and the effect of thymectomy were compared between 27 elderly patients (Group 2) and 119 young adult patients (Group 1) with myasthenia gravis (MG). In the elderly group, MG was type I in 3 patients, type IIA in 6, type IIB in 17, and type III in 1; and in the young group, type I in 6, type IIA in 36, type IIB in 73, and type III in 4. The association rate with autoimmune disease in patients without thymoma was 12.5% (1/8) in Group 2 and 21.3% (20/94) in Group 1. Autoimmune diseases were not seen in any patients with thymoma. The clinical stage of thymoma was not significantly different between the two groups. The rates of remission and of palliation at 3 years after thymectomy were 18.2% and 72.7%, respectively, in Group 2 patients with thymoma, 21.4% and 78.6% in Group 1 patients with thymoma, 50% and 100% in Group 2 patients without thymoma, and 50% and 98.1% in Group 1 patients without thymoma.