Forty-one specimens with pulmonary atresia and confluent pulmonary arteries were studied to establish the frequency and the nature of anomalies of both the ductus arteriosus and the central pulmonary arteries and their possible interrelation. The specimens were divided according to the type of pulmonary atresia: valvar atresia (12 cases) versus "muscular" atresia of the pulmonary orifice (29 cases). Abnormal connexions between the duct and the adjacent great arteries, as well as stenosis of a pulmonary artery, were common in cases with atresia of the pulmonary orifice and relatively rare in cases with imperforate valve. The abnormal connexions consisted of a proximal displacement of the origin of the duct from the aorta and displacement of the entry site of the duct into the pulmonary trunk towards one of the main pulmonary arteries. A left duct thus connected to the left and a right duct to the right pulmonary artery. Pulmonary artery stenosis, exclusively occurring in those specimens with a duct connecting to a pulmonary artery, were located in the segment of pulmonary artery between the pulmonary trunk and the duct. Histological examination revealed ductal tissue in the wall of a pulmonary artery in more than half of the cases with atresia of the pulmonary orifice. Ductal tissue in a pulmonary artery and pulmonary artery stenosis frequently coexisted. It is concluded that stenoses in the central pulmonary arteries may be related to the duct. The relationship resembles that between the duct and coarctation of the aorta.