Studies were undertaken of the cineangiograms in 196 consecutive patients entering two institutions with tetralogy of Fallot and pulmonary stenosis, none of whom had previously undergone a surgical procedure. The median age of the patients at the time of the study was 5.9 months. The diameters of the right ventricular infundibulum, pulmonary trunk, and the entirety of the right and left pulmonary arteries were measured (in millimeters), corrected for magnification, and expressed in standard deviation units (Z-values). The median values of the cineangiographically determined diameters of the right ventricular infundibulum and pulmonary trunk were smaller than those of 95% of normal individuals. The median values throughout the right and left pulmonary arteries were within the range of normal. Those of the distal branches of both the right and left pulmonary arteries were similar to the mean values in normal individuals. However, great variability of the dimensions between individuals, and along the pathway in individuals, characterized patients with tetralogy of Fallot. Diffuse narrowing of the pathways both proximally and distally was uncommon. The relation between the diameters of the pulmonary "anulus" and of the distal pulmonary trunk and origin of the left pulmonary artery explained the difficulty of extending an enlarging patch into a wide area distally in some patients.