Data from 35 patients with supravalvular aortic stenosis or pulmonary artery stenosis, or both, undergoing cardiac catheterization between 1973 and 1989 were analyzed retrospectively. Twenty-seven patients had supravalvular aortic stenosis: 11 required surgery after the first investigation and 8 (80%) of 10 others undergoing serial investigation showed an increase in the left ventricle to aorta pressure gradient. Angiographic measurements showed that the increase in the aortic pressure gradient was related to failure of normal growth of the ascending aorta lumen. Nineteen patients had pulmonary artery stenosis, with a right ventricular pressure greater than 33 mm Hg. At restudy, right ventricular pressure had decreased in 9 (82%) of 11 patients. This decrease in right ventricular pressure was associated with an increase in the systolic distensibility of the proximal pulmonary arteries, although there was no increase in the diastolic diameters. One patient had a rapid early increase in right ventricular pressure and no pulmonary artery growth. In two patients, multiple peripheral pulmonary artery stenoses became evident with time and produced persistent right ventricular hypertension. Supravalvular aortic stenosis is usually a progressive lesion, with an increase in left ventricular outflow tract pressure gradient related to poor growth of the ascending aorta. Pulmonary artery stenosis usually improves and only rarely limits prognosis.