Twenty-five newborns and infants aged < 1 year with the scimitar syndrome and pulmonary hypertension from 12 European pediatric centers were examined. Cardiac failure and severe respiratory insufficiency were always present. In 23 cases, pulmonary hypertension was due to a large shunt between abnormal arteries originating from the abdominal aorta and supplying the lower part of the right lung (vascular sequestration). In the last 2 cases, pulmonary hypertension was secondary to stenosis of the common trunk of the right pulmonary veins. Three of 10 patients who received only medical treatment survived; 2 are doing well, with pulmonary arterial pressures that have returned to normal, and the other had severe residual pulmonary hypertension. Six of 15 patients who underwent surgery survived. There were 5 ligations of a patent ductus arteriosus with 5 deaths, 3 pulmonary resections with 2 deaths, 1 dilation of a tight stenosis of the common trunk of the right pulmonary veins with 1 death, and 6 ligations of the abnormal arterial vessels with 5 surviving patients who are in good condition. Ligation of the abnormal arterial vessels appears to be the best type of treatment.