This study was based on 206 patients with non small cell lung cancer and N2 nodal disease submitted to curative surgery: pneumonectomy 163, lobectomy 39 and segmentectomy 4. All accessible mediastinal lymph nodes were removed and classified according to their anatomical location in lymph node chains; "skip" metastases were present in 24.8% of cases. N2 disease would have been missed in 20% of cases if routine removal of mediastinal nodes had not been performed. There was solitary nodal chain involvement by metastasis in 126 cases (61.2%). Overall 5-year survival was 18.3% +/- 3. Survival was not influenced by site, size or extension (T) of tumor, adjuvant radiotherapy, tumor histology or presence of vascular invasion. The prognosis was significantly worsened by the presence of microscopic residual disease (22 cases) and of satellite nodules (18 cases). Survival was significantly improved when metastases involved a single node chain (25% versus 8.5%). The location and number of involved nodes in the chain, "skip" metastasis and presence of extracapsular spread of carcinoma did not influence prognosis. Routine mediastinal lymph node dissection is necessary to improve survival and for classification of lung cancer. Anatomical description allows better understanding of N2 disease which is not a contraindication to surgery when a complete gross resection can be achieved.