Author made a clinical study of 48 cases of primary mediastinal tumors experienced in the dept. of the thoracic and cardiovascular surgery of Pusan National University Hospital during the 12 years period from march 1978 to march 1989. There were 34 males and 14 females. Their age distribution was from 4 months to 70 years, with the mean age of 34.4 years. 8.3 % of the patients were younger than 15 years old. There were teratoma 14 cases[29%], thymoma 11 cases[23%], neurogenic tumor 10 cases[21 %], lymphoma 6 cases[13 %], benign cyst 6 cases[13 %], and one case of fibrous histiocytoma in the histological distribution. The malignant tumors were 12 cases[25 %]. The common symptoms were chest pain and discomfort[35.4], coughing[18.8], general weakness and dyspnea. 16.7% of the patients were asymptomatic at admission. The successful removal was done in all cases of benign mediastinal tumors. In malignant cases, the surgical removal could be done in 5 cases. There was not postop. mortality. The frequent complications were atelectasis, infection, bleeding.