Eighteen patients with thymoma have undergone surgical treatment at Pusan National university Hospital from 1983 to 1993. The mean age of the patients was 47.3$pm$13.3 years old and male to female ratio was 1.6 : 1. Eleven of the patients[61.1%] with thymoma had myasthenia gravis; 12 cases[66.7%] were encapsulated and 6[33.3%] invasive. Operation was complete resection in 14[77.8%] of the patients, partial resection with residual tumor in 3[16.7%], and simple biopsy in one[5.5%]. Adjuvant radiotherapy was administered in 5 of 6 invasive thymoma. Postoperatively one patient died for excessive bleeding and sepsis. A tumor relapse was observed in one patient who had invasive thymoma and underwent partial resection followed by postoperative radiotherapy. The overall 5-year survival rate was 88.2$pm$ 7. 9%.The presence of myasthenia gravis is not considered as an adverse factor for survival but it contributes to early discovery of associated thymoma.