By means of lymph mapping, the prognosis significance of lymph node metastasis in lung cancer was studied in 270 patients who had undergone radical operations--pulmonary resection combined with complete mediastinal lymph node disection, which is used for patients in whom all cancer could thereby be ablated. Mediastinal lymph node metastasis was found in 64 patients, and 12 patients lived 5 years or more (an absolute 5 year survival rate of 18.8 percent). After radical surgery, there was a significant difference between the prognosis for patients who had metastases to the subcrainal lymph nodes as compared to the prognosis for those who did not. The 5 years survival rates were 9.1 percent and 29.0 percent, respectively. On the other hand, prognosis was not significantly affected by involvement or noninvolvement of the superior mediastinal, paratracheal, tracheobronchial, pretracheal, and the subaortic and para-aortic lymph nodes. No significant difference in survival was detected between patients who were given adjuvant therapy and those who were not. Lymph node mapping gives valuable prognostic information.