Thirty patients with myasthenis gravis[MG] underwent transternal extended thymectomy between 1983 and 1992 in Pusan National University Hospital. The age of patients was 11 to 62 years[mean; 35.2 years] with female dominant[M: F=l: 4]. According to modified Osserman classification, group I was in 6, II A in 7, II B in 13, III in 2, IV in 2 patients respectively. Their clinical response to thymectomy was evaluated. The follow-up period ranged from 2 months to 9.5 years[average; 51.3 months]. Fourteen patients[13.3%] had remission and eleven[43.3%] were improved after operation; half of patients were benefited from operation. Twenty patients had thymic hyperplasia and seven had non-infiltrating thymoma. In thymomatous MG one patient had remission and five were improved. Postoperative death was in a female patient. The cause of death was respiratory failure in the severe generalized MG preoperatively.