Objective: Purposes of this study were: 1) to compare mortality and postoperative morbidities (intra-abdominal abscess, wound dehiscence, and intestinal stricture) in extremely low birth weight (ELBW) infants who underwent initial laparotomy or drainage for necrotizing enterocolitis (NEC) or isolated intestinal perforation (IP); 2) to determine the ability to distinguish NEC from IP preoperatively and the importance of this distinction on outcome measures; and 3) to evaluate the association between extent of intestinal disease determined at operation and outcome measures.Background: ELBW infants who undergo operation for NEC or IP have a postoperative, in-hospital mortality rate of approximately 50%. Whether to perform laparotomy or drainage initially is controversial. Also unknown is the importance of distinguishing NEC from IP and the current ability to make this distinction based on objective data available prior to operation.Methods: A prospective, multicenter cohort study of 156 ELBW infants at 16 neonatal intensive care units (NICU) within the NICHD Neonatal Research Network.Results: Among the 156 enrolled infants, 80 underwent initial peritoneal drainage and 76 initial laparotomy. Mortality rate was 49% (76 of 156). Ninety-six patients had a preoperative diagnosis of NEC and 60 had presumed IP. There was a high level of agreement between the presumed preoperative diagnosis and intraoperative diagnosis in patients undergoing initial laparotomy (kappa = 0.85). The relative risk for death with a preoperative diagnosis of NEC (versus IP) was 1.4 (95% confidence interval, 0.99-2.1, P = 0.052). The overall incidence of postoperative intestinal stricture was 10.3%, wound dehiscence 4.4%, and intra-abdominal abscess 5.8%, and did not significantly differ between groups undergoing initial laparotomy versus initial drainage.Conclusions: Survival to hospital discharge after operation for NEC or IP in ELBW neonates remains poor (51%). Patients with a preoperative diagnosis of NEC have a relative risk for death of 1.4 compared with those with a preoperative diagnosis of IP. A distinction can be made preoperatively between NEC and TP based on abdominal radiographic findings and the patient's age at operation. Future randomized trials that compare laparotomy versus drainage would likely benefit from stratification of treatment assignment based on preoperative diagnosis.