Forty-infants were diagnosed as having necrotizing enterocolitis (NEC) during a 33 months' period; these represented 4% of all neonatal admissions. Pathological confirmation was obtained at surgery in 12 cases and at autopsy in 11, In the case of 21 infants who recovered without operation, the diagnosis was based on clinical and radiological criteria inculding the presence of intramural gas. NEC occurred primarily, though not exclusively , in low-birth-weight infants. Two-thirds of the infants developed NEC in the first week of life. Clinical features attributable to gastrointestinal malfunction as well as a systemic illness could be defined. Complications included pneumoperitoneum (34%), localized peritonitis as suggested by the development of an abdominal mass (11%) and intestinal obstruction (25%). Fourteen of the 15 cases of pneumoperitoneum were diagnosed within 24 hours after the onset of NEC. The 5 infants were localized peritonitis, who were managed conservatively initially, developed intestinal obstruction during recovery. Intestinal obstruction presented between 2 and 7 weeks after the onset of NEC. The overally mortality was 25%, infants with intestinal perforation or obstruction having and increased mortality of 38%.