Necrotizing enterocolitis (NEC) may be diagnosed radiologically when pneumatosis intestinalis or hepatic-portal gas are present on abdominal roentgenograms. Of 136 patients with strictly documented NEC, 19 (14%) never demonstrated specific roentgenographic evidence of NEC. The diagnosis in these 19 patients was, however, confirmed by a histopathologic examination of tissue obtained at the time of laparatomy or autopsy. In 13 of these infants gastrointestinal (GI) perforation developed 12 hours to eight days following the onset of symptoms, while in five patients ascites developed as the only roentgenographic sign of potential intra-abdominal disease. We do not suggest that the vast majority of infants with mild abdominal distention or positive for occult blood have NEC. However, differentiating NEC from these other more common GI problems (such as feeding intolerances) is presently difficult in the absence of definitive roentgenographic evidence of pneumatosis intestinalis or histologic examination of the involved tissue.