• We reviewed 2856 multiple-gestation pregnancies from 1980 to 1985 to identify whether birth order or other features (eg, asphyxia) were significant risk factors for the development of necrotizing enterocolitis (NEC). There were 42 infants identified as having NEC from 30 pairs of twins and three sets of triplets. The firstborn was diagnosed with NEC in 19 (45%) of the cases, with the disorder occurring in the secondborn in 23 cases (55%). While infants A and B were simultaneously affected in nine cases, among the three sets of triplets, no thirdborn infants developed NEC. Although the secondborn infants had significantly lower one-minute Apgar scores and a more frequent need for resuscitation, they were no more prone to develop NEC than were firstborn infants. Multiple gestation, birth order, feeding practices, and a number of other features we evaluated were not associated with the development of NEC. Our findings support the contention that prematurity is the only consistent risk factor in the development of NEC.