Persistent patency of the ductus arteriosus (PDA), common in premature infants, is associated with severe respiratory distress. The likelihood and significance of finding PDA in premature infants beyond the second week of life is unknown. We retrospectively analyzed all echocardiograms obtained between 1987 and 1992 on infants <35 weeks' gestational age. Of 446 echocardiograms 77 were obtained from infants >/=14 days. Of the 77 infants, 17 (22%) were found to have PDA (group 1) and the remainder did not (group 2). Forty-eight infants had been diagnosed as having PDA prior to 14 days of age. Of these infants, 16 were from group 1. Thus only 1/17 (6%) infants diagnosed as having PDA after 2 weeks did not have a history of PDA. The presence of PDA after 2 weeks did not relate to duration of oxygen therapy, ventilator therapy, or hospital stay. Furthermore, late closure of PDA in a subgroup of 11 infants did not appear to affect these parameters. It was concluded that premature infants beyond the second week of life are unlikely to have PDA if PDA had not been diagnosed during the first 14 days. Closure of PDA beyond the second week may not improve the infant's respiratory status.