A large series of cases of right aortic arch was studied clinically, pathologically, and roentgenologically. It was found that there are 2 types of right aortic arch, an anterior and a posterior. The anterior arch is almost invariably associated with cyanotic congenital heart disease while the posterior is usually an isolated anomaly. On the few occasions that congenital heart disease accompanies the latter, it is of the noncyanotic variety. It was found to be possible from the roentgen findings to predict in many instances the arrangement of the great vessels arising from the right arch.