Clinical variables (from the history, physical examination, electrocardiogram and chest radiograph) were related to the pressure gradient measured between the left ventricle and the aorta in 434 young patients with congenital valvular aortic stenosis admitted to a national collaborative study. The aim was to devise a composite clinical criterion for the recognition of patients with a small pressure gradient, so as to expand the opportunity for avoiding cardiac catheterization in such patients. Flattened or inverted T waves in lead V6 were found to be inconsistent with mild disease. Therefore, a composite criterion, providing an estimate of pressure gradient, was developed for patients without T wave changes. The final criterion, based on multivariate analysis, involved only the intensity of the systolic murmor, the presence or absence of an early diastolic murmur, and voltages of the Q and R waves in lead V6. Patients with a low estimate by this procedure rarely had a large measured gradient. Only 3.7 percent (6 of 161) with an estimated gradient of less than 45 mm Hg had a gradient at cardiac catheterization of 80 or more mm Hg; none (0 of 32) with an estimated gradient of less than 30 mm Hg had a gradient of 50 or more mm Hg. This criterion should be helpful in avoiding unnecessary catheterization by identifying some patients with valvular aortic stenosis who have a small pressure gradient.