The systematic application of roentgenologic criteria here proposed permits the objective classification of patients with congenital heart disease. The basic criterion is the degree of pulmonary arterial vascularity, which may be increased, normal, or decreased. The first class, marked by increased pulmonary vascularity, is the largest, it includes interventricular and interatrial septal defects, the most frequent congenital heart lesions. The second largest class, marked by decreased pulmonary vascularity, includes another frequently seen lesion, the tetralogy of Fallot. The third class, with normal pulmonary vascularity, includes such lesions as coarctation of the aorta. Conventional films and fluoroscopy may need to be supplemented by retrograde aortography and angiocardiography; in addition, roentgenographic findings during heart catheterization often give valuable diagnostic clues. Analysis of the roentgenologic features of a case, obtained by conventional x-ray examination without contrast, considered along with the simple clinical data, will generally yield a working diagnosis.