An outbreak of necrotizing enterocolitis, a condition in which a section of the bowel dies, occurred in a neonatal unit of a hospital in Belgium. Twelve infants became ill, and two died. Enterobacter sakazakii, also known as Cronobacter sakazakii, was found in stool samples taken from six of the twelve infants. Ten of the infants had been fed orally with the same brand of powdered milk formula. Enterobacter sakazakii was isolated from the prepared formula milk as well as from several unopened cans of a single batch of powdered formula. The strains of Enterobacter sakazakii from the infants were partially similar to the strains that were isolated from the formula. No additional cases of necrotizing enterocolitis occurred once this formula was removed. Microbiologic contamination of powdered formula was suggested to be a contributive factor in the development of necrotizing enterocolitis, a condition encounted almost exclusively in formula-fed premature infants.