A prospective study was performed analyzing the bronchial resection boundaries of 120 patients operated on for lung carcinoma. The resection boundary, maximum tumor diameter, distance between tumor and resection boundary, and lymph-node stage were analyzed by serial sections of the surgical specimens (lobes and lungs). The following results were obtained: 20/120 cases (17 %) displayed microscopic tumor invasion of the resection boundary (R1 status), most frequently adenocarcinoma (21 %). The R1 status was closely associated with the distance between tumor and resection boundary and postsurgical lymph-node stage (pN stage): all 8 tumors excised at distance 1 mm or less from the bronchial resection boundary revealed bronchial submucous tumor growth, whereas none of the tumors located more than 20 mm from the resection boundary was found to display tumor invasion of the bronchial boundary. Curative resection was noted in all 40 tumors operated at pNO stage and in only 11 cases (69 %) of tumors with distant lymph-node metastases (pN3 stage). No relationship between tumor infiltration of the resection boundary and type of resection was seen. The data indicate that a) intra-operative control of bronchial resection boundaries is necessary in all lung-carcinoma patients with central tumor localization less than 20 mm from the proposed resection boundary; b) a ''safety distance'' between resection boundary and tumor boundary is of specific importance in bronchial carcinoma with lymph-node metastases.