• We examined the records of ten pairs of twins and one set of triplets among whom one or more infants had necrotizing enterocolitis (NEC). Perinatal asphyxia and respiratory distress were less common in the firstborn infants. It might, therefore, be anticipated that necrotizing enterocolitis was less common in this group. We found the reverse to be true. In all of the twin pairs twin A had NEC, and in no case did only twin B have NEC. The disease developed in triplet B but not in triplets A or C. Examination of associated risk factors revealed that the firstborn infants were more stable, were fed sooner, and had feedings advanced somewhat more rapidly than their counterparts. We reemphasize that there are unrecognized risk factors in the pathogenesis of NEC and that a high index of suspicion should be maintained for all premature infants despite their apparent stability.