The period from .1959 to 1976, authors experienced 13 cases of thymoma at the Department of Thoracic and Cardiovascular Surgery in National Medical Center. Ten patients were male, and 3 patients were female.Main complaints were cough 76.9%, dyspnea, 69.2%, chest pain 61.6%, myasthenia gravis 23.1 % and S.V.S 23.1%. All of them located anterior mediastinum. 7 cases were benign and 6 cases were malignant. Lymphocytic type was 5 cases, epithelial type 3 case,spindle cell type 1 case, mixed type 2 cases, cystic type 1 case and seminomatous type 1 case. All cases were surgically approached but in malignant cases, only 1 case was palliatively removed and followed radiation therapy. 4 cases were made only biopsy, among them, obstained good response with radiation therapy in seminomatous type case. In benign cases, excellent result was obtained but 2 cases which were combined myasthenia gravis were relapsed the symptoms.[KTCS 1977;2:355-358]