Agenesis of the intrapulmonary and extrapulmonary veins of the right lung was found by angiography and histological examination in a three year old boy. Blood supplied by the intersegmental arteries drained via the pulmonary arteries of the right lung into main and left pulmonary arteries. This caused a shunt between the aorta and pulmonary artery. Agenesis of the pulmonary venous system as a cause of left to right shunt has not been reported before.