In the past 25 years, 1,654 patients with non-small cell cancer underwent resection at National Cancer Center Hospital, Tokyo. A comparative study has been made of 5-year survival of patients who had pulmonary resection with and without mediastinal lymph node dissection. There were 426 patients (25.8% of the total) with N2 M0 disease. Of these, 345 underwent pulmonary resection with mediastinal lymph node dissection. The 5-year survival in this group was 15.9% (T1 N2 M0, 30.0%; T2 N2 M0, 14.5%; and T3 N2 M0, 12.9%). In the remaining 81 patients, who did not have mediastinal lymph node dissection, 5-year survival was 6.7%. Of the 426 patients with N2 M0 disease, 242 were select patients who underwent a curative operation with an overall 5-year survival of 19.2%. Sixty-six of them had squamous cell carcinoma and a 5-year survival of 30.8%; 153 had adenocarcinoma and a survival of 16.0%; 14 had large cell carcinoma and a survival of 12.8%; and 9 had adenosquamous cell carcinoma, and none survived 5 years. To improve the end results, it is important to perform as many curative operations with mediastinal lymph node dissection as possible. Histological cell type and tumor status must be taken into consideration.