Congenital right diaphragmatic hernia can present a difficult diagnostic problem. An illustrative case is reviewed in which the diagnosis was not con sidered during the initial hospitalization because chest radiographs were inter preted as showing an atelectatic and pneumonic process. Once suspected, the diagnosis was made by fluoroscopy, which showed an immobile right hemi diaphragm, and by liver scan, which demonstrated herniation of the liver into the right thorax. The tendency of congenital right diaphragmatic hernias to present after the neonatal period and to mimic pulmonary parenchymal dis ease is discussed. Several alternative means of diagnosis of right diaphragmatic hernias are reviewed.