Administration of anti-cholinesterase before operation and high doses of prednisolone after the operation are commonly prescribed in cases of thymectomy for the treatment of myasthenia gravis. Our policy is to carry out an extended thymectomy combined with pre- and post-operative administration of prednisolone on alternate days. Our method was used in the treatment of 50 patients with generalized myasthenia gravis, from January 1979 to December 1984. The results were examined in conjunction with the necessity for preoperative administration of an anti-cholinesterase preparation and also with factors influencing the follow-up result and postoperative process. This method made it feasible to perform surgery under conditions of stabilization of clinical symptoms and satisfactory postoperative management. A postoperative period of unstable symptoms could thus be avoided. The palliation rate at one year after the operation was 96 per cent, while the remission rate at 5 years after the operation was 70 per cent. The preoperative supplement of anti-cholinesterase and preoperative per cent forced vital capacity were considered to be predictive factors concerning the necessity of artificial respiration.