Accuracy of the radiologic diagnosis of emphysema was assessed in 696 patients from whose lungs paper-mounted whole-lung sections had been made. Emphysema was diagnosed radiographically primarily on the basis of arterial deficiency. In addition, lung length, lung width, size of the retrosternal space, heart size, and diaphragm position were recorded from the chest films. Recognition of emphysema was poor when radiographs of inadequate quality were included (anteroposterior films or films from patients with acute or chronic lung disease). When these films were excluded, only occasional radiographs from patients without emphysema or with mild emphysema were thought to have emphysema radiologically. Of the patients with moderately severe and severe emphysema, 41% were diagnosed as having emphysema, as were two-thirds of those with the most severe grade of emphysema. For a given grade of emphysema, the radiologic diagnosis of emphysema was made more frequently when patients had severe chronic airflow obstruction. Emphysema was usually most severe in the zones of the lung in which emphysema was radiologically apparent. Centrilobular emphysema was usually present when emphysema was diagnosed radiologically in the upper zones of the lung, and panacinar emphysema was usually present when emphysema was diagnosed in the lower zones. Lung length and the size of the retrosternal space increased, the level of the diaphragm lowered, heart size decreased, and lung width was unchanged as emphysema became more severe. Lung length and diaphragm level were the most discriminating measurements, followed by size of the retrosternal space. No combination of radiologic variables was found that recognized emphysema better than the subjective diagnosis of emphysema based on arterial deficiency. Radiologic lung dimensions are related to stature; for given stature these measurements are larger in men and women.