We compared findings on bronchoscopy, computed tomography (CT), and pathologic examination of the infiltrative surgical margin in patients with lung cancer. Of 397 patients operated on for primary lung cancer, 13 had a positive bronchial surgical margin (squamous cell carcinoma, 8 cases; adenocarcinoma, 4 cases; and small-cell carcinoma, 1 case). Nine of the 13 patients had stage III disease. Flexible bronchoscopic findings were classified according to the General Rules of the Japanese Lung Cancer Society. Nine of the 13 patients had bronchial wall abnormalities, indistinct cartilage rings, or unopened bronchial spurs. On CT, 9 of the 13 patients (69%) had thickened or narrowed bronchial walls or swollen adjacent lymph nodes. On pathologic examination, infiltration was superficial in 5 patients, sub epithelial in 2, intramural in 2, and extramural in 4. Eleven of 13 patients (84%) had some evidence of disease at the bronchial surgical margin on bronchoscopy or CT of the chest. We conclude that comparison of findings on bronchoscopy and chest CT is useful to determine the bronchial margin in lung cancer patients.