Myasthenia 8ravis is a disorder of neuromuscular function due to a reduction of available acetylcholine receptors at the neuromuscular junction. Typically, the muscle weakness is worse after effort and improved by rest. In 1939, Blalock and associated reported a case of patient with myasthenia gravis who was successfully treated by thymectomy. Since then, operation has become increasingly important in the management of this disease. From 1968 to 1983, 10 cases of myasthenia gravis were operated at the Department of Thoracic and Cardiovascular Surgery,College of Medicine, Seoul National University. 1.Among 10 cases, 4 were male and 6 were female. 2.Thymectomy was performed in 9 cases, and 1 case of malignant thymoma with deeply infiltration to adjacent structure was not resectable. 3.There was 1 operative mortality with respiratory failure. 4.During follow-up period, most of them showed symptomatic improvement, but complete remission was not noticed in any case.