Among tumors of the lung, main stem bronchial cancer offers a particularly unfavorable prognosis, probably because of its rapid extension to the segmental bronchi, trachea, and extrapulmonary structures. However, analysis of data gathered by the End Results Group indicates that survival among those patients with main stem bronchial cancer whose tumor was resected was virtually the same as that of patients with resectable lung cancer of other sites. From these data it is impossible to assess what role, if any, the resection itself played, and a randomized trial would be necessary to determine whether resection improves the probability of patient survival. On the other hand, it is not now advisable to deny resection to patients with operable main stem bronchial tumors (except oat cell tumors) on the basis of the available nonexperimental evidence alone.