Forty-four infants were diagnosed as having necrotizing enterocolitis (NEC) during a 33 months' period; these represented 4% of all neonatal admissions. An increase in incidence was observed during this period, particularly in low-birth-weight infants weighing under 1,500 g. Perinatal risk factors occurring in infants preceding their onset of NEC are found also to be significantly more common in infants under 1,500 g compared with those between 1,500 and 2,499 g. When the incidence of these clinically associated conditions in infants with NEC are compared with the incidence in infants who did not have NEC in the same birth weight category, a difference can be demonstrated only in 4 out of the 23 analysed: prolonged rupture of membranes with amnionitis; birth asphyxia; hypertonic milk feeds; exchange transfusion. As NEC is possibly a disease of multifactorial aetiology, a multivariant analysis of the data is indicated to define the role of combined perinatal risk factors in the pathogenesis of this disease.