Owing to the rather large number of recent reports on primary cancer of the lung, another contribution may seem to be an unnecessary addition to the already extensive literature. As we review this subject and reflect on past experiences, we suspect that many cases may have been overlooked owing to a lack of complete understanding or an inadequate study of the material. Particularly was this true a decade or more ago when the disease appeared to be more or less a rarity. Recently there has been a reported increase in cancer of the lung to a figure approaching 2 per cent of all patients coming to autopsy. Wells1 said, "There seems to be little doubt that primary cancer of the lung is now a more common disease in Europe and America than it was even ten or fifteen years ago." The disease appears to be so common that it