SimplyThick(®)(ST) has been safely used as a thickener to treat adults who have dysphagia, but the safety of this product has not been studied in premature infants. Xanthan gum is the ingredient in ST that results in thickening and also is an effective laxative. We recently began using ST to treat premature infants with dysphagia and/or gastroesophageal reflux. We describe three cases of premature infants who developed necrotizing enterocolitis (NEC) after they were fed ST. Unlike classic NEC, all three cases presented with late-onset colonic NEC.