Recent reports have emphasized the high and apparently increasing incidence of primary carcinoma of the lung.1At the Cleveland City Hospital in the eleven year period from 1927 to 1937, inclusive, there were 100 cases in which autopsy was performed, which constitute 1.3 per cent of 7,685 consecutive cases studied post mortem and 9.4 per cent of 1,064 cases of malignant tumor studied post mortem. At autopsy the lung ranked second only to the stomach as the primary site of carcinoma. While such a postmortem incidence obviously does not represent the true morbidity for the entire population, it serves to reflect again the frequency and importance of this tumor. A summary of the salient gross and microscopic observations in these 100 cases of primary bronchiogenic carcinoma studied post mortem constitutes the substance of this paper. The attempt will be made to correlate the cell type of the tumor with