We review our experience with unresectable non-small cell lung cancer, after adoption of a more aggressive surgical approach, including mediastinal lymph node dissection. Cases with enlarged mediastinal lymph nodes (MLNs, cN2) that were predicted to be resectable were included. Our objective was to identify preoperative findings to prevent unnecessary thoracotomy. In 1988-1997, 192 patients had thoracotomy for non-small cell lung cancer. Fifteen cases (7.7%) were found unresectable at thoracotomy. CT scans demonstrated enlarged MLNs in 7 of 15 and enlarged hilar lymph nodes in 6 of 15 cases. The tumor abutted the hilum in 5 of 15, chest wall in 2 of 15, and mediastinal structures in 7 of 15 cases. Atelectasis was seen in 3 of 15 cases. During the same period, 63 patients with stage III disease, including 39 patients with enlarged MLNs, were resected. The unresectability rate for cN2 patients was 15.2 per cent. Five (33%) patients were physiologically unable to tolerate the required pneumonectomy [forced expiratory volume in 1 second, 1.65 liters (range, 1.15-2.07)]. There were three (20%) esophageal invasions, two (13.3%) mediastinal invasions, two (13.3%) aortic invasions, two (13.3%) metastases to the diaphragm, and one (6.6%) invasion of proximal pulmonary artery. Median survival was 4 months. Two-year actuarial survival was 8 per cent. We conclude that careful palpation and dissection were required to establish unresectability. Preliminary thoracoscopy would have prevented thoracotomy in two cases (13.3%) of diaphragmatic metastases but would not reliably establish unresectable invasion of mediastinal structures.