In the operating room, 66 preterm infants weighing between 710 and 2,700 gm (23 less than 1,000 gm) underwent ligation of a patent ductus arteriosus (PDA). Respiratory distress syndrome was present in 53 patients; the rest had apnea-bradycardia syndrome. PDA ligation was indicated for intractable congestive heart failure in 52 patients or progressive respiratory failure in 14. There were no intraoperative deaths. Fifteen infants died 1 to 120 days postoperatively. Seven deaths resulted from intracranial bleeding, 3 from diffuse coagulopathy, and 1 from respiratory failure. The condition of patients with heart failure improved postoperatively, with the mean left atrium to aorta ratio reduced from 1.56 to 1.02 (p = 0.05). Respiratory function improved in 25 patients extubated by the third postoperative day. Late follow-up (one to five years) of the 51 survivors showed 1 late death. Seventeen survivors had roentgenographic evidence of bronchopulmonary dysplasia. Infants with bronchopulmonary dysplasia required longer postoperative ventilation (mean, 21.5 days compared with 4.75 days). Twenty-four infants were normal. Ligation of PDA in preterm infants has low intraoperative risk and improves the condition of those with heart and respiratory failure. Late follow-up showed good recovery of nearly two-thirds of the patients.