In order to evaluate the prognostic significance of the preoperative assessment of mediastinal lymph nodes, 100 patients with potentially operable lung cancer underwent two-plane tomography, computed tomography (CT), transbronchial needle aspiration (TBNA; 47 patients), and cervical mediastinoscopy. Mediastinoscopy proved to be the most accurate staging procedure. Tomography was less specific, detecting only advanced mediastinal node involvement, and CT was as sensitive as mediastinoscopy but sensibly less specific. TBNA gave no false positive results but a false negative rate of 25.5 percent. Accurate preoperative staging of mediastinal nodes is mandatory to optimize the resectability rate of lung cancer. Where metastatic involvement of mediastinal nodes was preoperatively documented at more than one level, tumors were invariably unresectable. Mediastinoscopic demonstration of intracapsular metastases at only one level did not preclude complete resection. Before thoracotomy, confirmation of neoplastic spread to mediastinal nodes suggests very low survival rates, especially in patients with incomplete removal of tumors.