One hundred fifty-three patients with bronchogenic carcinoma were evaluated prospectively by CT and mediastinoscopy. Nodes larger than 5 mm were considered potentially metastatic. All results were correlated with surgical findings. Computed tomography is more sensitive (89%) in the detection of mediastinal metastases than mediastinoscopy (67%). Computed tomography has a poor predictive value (47%); however, a negative examination is highly accurate (89%). Within a group of 100 node sites, 72% of the nodes involved by tumor were larger than 1 cm in diameter. Squamous cell carcinoma and adenocarcinoma have the highest percentages of sensitivity by CT. The very low incidence of metastatic involvement in nodes under 5 mm allows one to forego mediastinoscopy in the presence of a negative CT.