In our attempt to band the main pulmonary artery above the valve in a 4-month-old prematurely born infant, we erroneously banded only the left pulmonary artery, owing to the unusually low origin of the right pulmonary artery (which arose partially in the sinus of Valsalva). When severe cardiac failure recurred, the anomaly was noted upon reoperation and the band was repositioned at the level of the pulmonary valve. Since this revision, the postoperative course has been good. Low origin of the right pulmonary artery is normal in premature infants. However, origin of the right pulmonary artery from the sinus of Valsalva is a sufficiently extreme variant to constitute a surgically important anomaly. Our postmortem studies of the pulmonary arteries of 25 premature infants born without cardiac malformation showed that while the right pulmonary artery was lower than the left, it never originated from the sinus of Valsalva. This anomalous configuration of the pulmonary arteries has, to our knowledge, never been found in an infant as old as 4 months; yet we believe it should be taken into account when banding pulmonary arteries in infants.