Eighty-seven infants (0.13% of livebirths) developed necrotizing enterocolitis (NEC) during a 15-year period at the Mercy Maternity Hospital, Melbourne. The disease was associated with 23 deaths, representing a mortality rate of 26.4% and comprising 2.6% of all neonatal deaths. The incidence of NEC increased from 0.07% of all livebirths for the years 1971-1974 to 0.25% for the 19-month period from January, 1984 to July, 1985. The mean age at onset was 9.9 days with an inverse relationship between birth-weight and age of onset of the disease. The mothers of the infants who developed NEC belonged to a significantly higher risk obstetric population; gestational diabetes was identified in 3 of 28 mothers (10.6%) having glucose tolerance tested, and 1 other patients was a known diabetic. Subnormal oestriol excretion was detected in 15 of 45 patients tested, treble the overall hospital incidence. Of the 87 infants, 26 (29.9%) were VLBW (birth-weight less than 1,500 g), 5 were term (5.7%) and 9 (10.3%) were small for gestational age. The mean gestational age was 34.7 weeks and mean birth-weight was 1,988 g. Sixty-seven (77%) infants received medical treatment alone and 20 (23%) also received surgical treatment. Sequelae which developed in survivors were colonic strictures (4), fistulas (2) and the short-gut syndrome (1).