There has been arguing in the proper surgical treatment of myasthenia gravis. But the ultimate goal of operation is complete removal of thymic tissues. In view of previous surgical-anatomic studies that there are frequently thymic tissues from the level of thyroid gland to the diaphragm and from hilum to hilum, en bloc resection of thymus, mediastinal fat including both sheets of pleura and pericardium is reasonable. We experienced four myasthenic patients with radical thymectomy from 1989. As compared to the result of previous simple thymectomy group, the 23 patients who were operated from 1976 to 1988[Group I ], excellent surgical outcome was obtained in radical thymectomy group[Group II ].