The mediastinoscopy was a well known useful diagnostic tool for detection of mediastinal lymph nodes invasion by bronchogenic carcinoma, and also useful means for histologic diagnosis of metastatic carcinoma and certain mediastinal tumors. 31 cases of mediastinoscopies were reviewed which were experienced at Kyung Hee University Hospital from July, 1979 to June, 1985. We experienced 20 cervical mediastinoscopies, 10 left anterior mediastinotomy, and 1 both procedures. Of the 31 cases, 22 cases were used for preoperative staging of bronchogenic carcinoma, 7 cases for mediastinal tumor diagnosis, and 2 cases for histologic diagnosis of metastatic carcinoma. In 22 mediastinoscopies which were used for preoperative staging, 10 cases were revealed positive mediastinal nodes, and could avoid meaningless thoracotomy. All 12 mediastinoscopy negative patients were received thoracotomy, and 10 of them were resectable. The resectability in bronchogenic carcinoma was 83%, on the contrary, the other series at premediastinoscopic era revealed only 65% resectability. Other mediastinal lesions such as tuberculous granuloma [4], sarcoidosis [2], malignant thymoma [1], and metastatic carcinoma [2] were also diagnosed successfully. Mediastinoscopy is very useful tool for determination of treating method of bronchogenic carcinoma, and for diagnosis of certain mediastinal tumors which, otherwise, need a thoracotomy for confirmatory diagnosis.