The location, frequency, and spread of metastases to the mediastinal lymph nodes were examined in 124 patients with histologically proven N2 disease who underwent pulmonary resection and total lymph node resection. There were one-level metastases in 47 percent of cases, two-level metastases in 29 percent, three-level in 12 percent, and 12 percent had four or more levels of metastases. Nodal metastases to the lower mediastinum from upper lobe cancer were frequently observed as were metastases of lower lobe cancer to the upper mediastinum. The frequency of the latter was higher than that of the former. About one third of squamous cell carcinoma and adenocarcinoma in the right upper lobe produced nodal metastases in the lower mediastinum. In addition, there were often skip metastases to the nonregional parts of the mediastinum without regional nodal involvement in the mediastinum. From the results of the present study, it appears that extensive mediastinal dissection should be recommended in surgery for lung cancer irrespective of the location of the primary tumor.