Daily aortic contrast echo studies were carried out in 200 neonates with severe respiratory disease to determine the natural history of the ductus arteriosus during the first days of life and the effect of patency on subsequent morbidity and mortality. Decisions related to surgical or pharmacologic closure of a PDA were not based on the results of the contrast echo studies. The risk that intervention would be required was greater in infants weighing less than 1500 gm (P less than 0.005) and in patients in whom the ductus had not closed spontaneously by day 3 (P less than 0.001) regardless of birth weight. The clinical course in infants with a PDA on the third day of life revealed a lower survival rate (P less than 0.005), a greater requirement for prolonged respiratory support (P less than 0.005), and a higher incidence of bronchopulmonary dysplasia (P less than 0.005) in all birth weight categories. Ductal patency often was not associated with early clinical manifestations. No infant who had a negative echo study on the third day of life subsequently developed signs or symptoms of patent ductus arteriosus. We conclude that patency of the ductus arteriosus is a negative prognostic factor in the severely ill neonate with respiratory distress.