The timely distinction between infants with necrotizing enterocolitis (NEC) who need surgery and those who are likely to recover with medical management is important, but it may be difficult clinically. Because pneumoperitoneum is not always present, additional markers of bowel gangrene are needed. Among 73 babies managed for NEC over the study period, 49 (67%) met the study criteria of Bell's stage > 1, and their records were reviewed to determine the usefulness of common laboratory tests in predicting outcome. The patients were divided into three groups based on management. Group 1 (7 patients) required surgery at the time of initial presentation because of pneumoperitoneum. The remaining 42 patients were initially managed medically, 19 of whom (group 2) recovered successfully; the other 23 (group 3) required surgery. The combination of certain laboratory tests, ie, white blood cell count (WBC), immature:total neutrophil ratio (I:T), platelet count (PLT), and base excess (BE), was of significance in distinguishing between infants who would need surgery and those who would recover with medical therapy (group 3 v group 2) 4 to 12 hours or 12 to 24 hours after the diagnosis of NEC was established. A scoring scale was developed, with a point for each of the following: WBC < 9,000/mm(3), I:T > .5, PLT < 200,000/mm(3), and BE less than or equal to -2. A score of greater than or equal to 3 during 4 to 12 hours after diagnosis of NEC strongly predicted the presence of surgical disease (positive predictive value, 100%; negative predictive value, 76%; specificity, 100%; sensitivity, 64%). This scoring scale, along with clinical course, can assist in determining the need for surgery in a timely manner. Copyright (C) 1994 by W.B. Saunders Company