Summary.Necrotising enterocolitis is the most common gastrointestinal complication of pre‐term infants. In order to determine the strength of the association of hypoxia/ischaemia and infection as causative factors in necrotising enterocolitis, we evaluated all liveborn pre‐term infants with a birthweight<1500 g and/or gestational age<32 weeks in The Netherlands in 1983. The factors related to hypoxia/ischaemia included: asphyxia, respiratory distress syndrome, ventilatory assistance, persistent fetal circulation, persistent ductus arteriosus, apnoea, bradycardia, exchange transfusion and peri/intraventricular haemorrhage; those related to infection were: congenital infections, pneumonia, sepsis and meningitis. Of the 1338 infants enrolled, 1187 survived for more than 24 hours and had complete data. Mean (pLs.d.) birthweight was 1278 (pL297) g and mean (pLs.d.) gestational age 30.7 (pL2.6) weeks. Seventy‐three (6.1%) infants developed necrotising enterocolitis: 46 (63.0%) stage I disease (clinically very suspect), 11 (15.1%) stage II (pneumatosis intestinalis) and 16 (21.9%) stage III (intestinal perforation). Mean pL s.d. birthweight of the infants with necrotising enterocolitis (1197 pL 284 g) was lower (P<0.02) than in those without necrotising enterocolitis (1283 pL 297 g). Gestational ages were comparable. Mortality in the group with necrotising enterocolitis was 21.9% versus 15.8% in the non‐necrotising enterocolitis group (NS). Stepwise logistic regression analysis indicated that among those factors studied, only sepsis and birthweight were truly associated with the occurrence of necrotising entero