During the 1940s and 1950s, as many as 50% of thoracotomies identified nonresectable tumors. At present, better than 90% of patients undergoing thoracotomy for presumably resectable lung cancer are found to have operable tumors. This improvement is the result of major advances in the preoperative staging of this disease. Mediastinoscopy and computed tomography (CT) are the most valuable techniques for evaluating the mediastinum in patients with primary cancer of the lung. For each modality, the primary objective is to define the presence or absence of spread to mediastinal lymph nodes. In patients with non-small-cell lung cancer, surgical resection remains the treatment of choice so long as all recognizable tumor can be removed at operation. Both mediastinoscopy and CT provide critical information concerning the potential for a complete resection. Computed tomography remains the most effective noninvasive technique for the evaluation of mediastinal nodes.