Thirty cases of congenitally corrected transposition of the great vessels are reported, including the first case without other cardiac anomalies (except congenital heart block) diagnosed in life on the basis of chest roentgenograms. The anatomy, embryology, and clinical and roentgeno-graphic features are briefly reviewed. Inversion of the primitive bulboventricular loop is responsible for the ventricular inversion typically present in this interesting cardiac malformation. Other malformations of the heart are nearly always associated. Appreciation of the anomaly is essential for interpretation of certain examples of mesocardia and dextrocardia. The abnormality should be suspected when any of the following conditions are present congenital heart block, mesocardia or dextrocardia without visceral situs inversus, a loud single pulmonary second sound in the presence of clinical pulmonary stenosis, and congenital insufficiency of the left atrioventricular valve. A peculiar straight or long convex contour to the left upper heart border on plain films is suggestive of congenitally corrected transposition, and angiocardiography is diagnostic.