A male infant, having a persistent fifth aortic arch and interruption of the aorta distal to the left subclavian artery, underwent successful surgical treatment. A histological study of the excised segment of the aorta showed that the ductal tissue extended to the junction between the fifth arch and the descending aorta with consequent narrowing in the corresponding region. The ductal tissue, however, did not contribute to occlusion in the fourth aortic arch. The morphogenesis of this combination of aortic arch anomalies was also discussed.