The use of computed tomography of the chest in mediastinal staging of lung carcinoma lies the premiss that malignant lymph nodes are larger than benign ones. We have studied the size of mediastinal lymph nodes & the malignancy rate in 55 lung carcinomas from March 1990 to July 1992 at the Department of Thoracic and Cardiovascular Surgery, Yongdong Severance Hospital, Yonsei University College of medicine. The lack of relationship between the size of mediastinal lymph node and the probability of malignancy helps to clarify the limitations of the use of computed tomography in the staging of the mediastinum in lung carcinoma. There was no tendency for all malignant lymph nodes to be larger than benign nodes. To allow comparison with our data, malignancy rates for all lymph nodes larger than 10mm are 24.8% in sensitivity & benign rates for all lymph nodes less than 10mm are 96% in specificity. But all mediastinal lymph nodes larger than 30mm are metastatic lymph nodes in our cases. We are going to try to have thoracotomy for complete resection of lung carcinoma as possible as we can if there no evidence of contralateral mediastinal metastases of lymph nodes, even though there are large mediastinal lymph nodes in lung carcinoma.