BRONCHOGENIC carcinoma has assumed a position of paramount medical importance because of its rapid increase in incidence. Statistics reveal that the incidence of bronchogenic carcinoma apparently is rising faster than that of any other visceral malignant condition in the male, and most authorities in the United States report an eight- or ninefold increase in yearly deaths from cancer of the lung. Although there has been a steady increase in operability rate, decrease in operative mortality, and amelioration in postoperative prognosis of the patient with bronchogenic carcinoma, further substantial improvement in the results of treatment depends on earlier, correct diagnosis. Confusion in proper recognition of carcinoma of the bronchus may be due to the coexistence of a benign pulmonary disease or simulation of a benign pulmonary lesion by the malignant process. The purpose of this exhibit is to present some of these problems in diagnostic differentiation and to review several clinical