The series presented consists of 25 babies (18 of which were neonates), seen between 1972 and 1974. The anatomical and angiographic study revealed 5 anatomical types, according to whether the pulmonary orifice was patent or atretic, and according to the size of cavity of the right ventricle, which may be normal or reduced (perhaps almost totally). The diagnostic clinical features and findings on angiography are recalled. The operative procedure in all 25 cases was pulmonary valvotomy carried out with a brief normothermic period of cirulatory arrest. The technique is described briefly. The results, which vary widely with the anatomical type, were as follows: out of the 25 operated cases there were 12 deaths during or immediately after surgery. The figures are none-the-less encouraging, given the grave natural history of this condition in the baby. The best results were seen in cases in which there was a right ventricular cavity of normal or at least acceptable size. The maximum postoperative follow-up period was 3 years. Most of these children have a persistant pulmonary stenosis and hypertrophic right ventricle, and require a second operation in early infancy.