Between January 1988 and December 1990, 132 neonates weighing < 800 g were admitted to our neonatal intensive care unit. Of the 76 who survived initial resuscitation, 42 had developed a hemodynamically significant patent ductus arteriosus (PDA) (mean +/- SD): gestational age 25.3 +/- 1.9 weeks, birth weight 650 +/- 93 g. Two infants were referred for primary surgical ligation because of contraindications to indomethacin. Forty infants were initially treated with indomethacin. Seventeen of 40 (43%) were subsequently referred for surgical ligation because of indomethacin failure. Infants requiring surgical duct closure were a lower gestational age (24.6 +/- 1.3 v 25.7 +/- 2.0 weeks, P = 0.49) and had a greater left atrial-aortic (LA/Ao) ratio on echocardiography (1.71 +/- 0.28 v 1.46 +/- 0.26, P = .04) compared with those treated successfully with indomethacin. There were 6 deaths (15%), all of which occurred in infants receiving indomethacin (5 indomethacin alone, 1 indomethacin+ligation). Indomethacin was directly associated with intestinal perforation in 3 patients, and acute renal failure in 1; all 4 died. Surgery was associated with minimal morbidity (intraoperative transfusion in 1, postoperative pneumothorax requiring chest tube in 1). These data suggest that in the extremely premature neonate with a hemodynamically significant PDA: (1) indomethacin therapy is associated with a high failure rate and significant complications; (2) PDA associated with a large LA/Ao ratio is unlikely to close with indomethacin therapy; and (3) surgical duct closure is associated with minimal morbidity. We conclude that primary surgical ligation may provide the optimal management for PDA in carefully selected patients.