Operations under direct vision for congenital aortic stenosis began with the use of hypothermia, but since heart-lung machines have become safe, cardiopulmonary bypass is now preferred. Today these 2 modalities are combined for the benefit of both patient and surgeon. Our purpose in this paper is to review our experience with operations upon 31 patients who had various types of congenital aortic stenosis. It has only been in the past 2 or 3 years that certain fine points in the differential diagnosis of the various types of aortic stenoses have been noted. In addition, the criteria for recommending operation are being more accurately defined. Children with aortic stenosis of mild to moderate degree are usually asymptomatic. When the stenosis is more severe, symptoms occur more frequently, but some of these children are also asymptomatic. Twenty-four of our patients had exertional dyspnea, syncope, or angina; 3 had symptoms only of fatigue.