Forty-three cases of neonatal necrotizing enterocolitis are reviewed, showing a recent incidence of almost 4 per cent among premature infants at this medical center. The onset is most frequent between days 2 and 5 following birth. The most common clinical manifestations are temperature instability, lethargy, gastric retention, abdominal distention, and guaiac positive stools. Pneumatosis intestinalis is the roentgenographic hallmark of NEC, being seen in 98 per cent of this series. Other important findings on routine abdominal roentgenography include rather nonspecific bowel distention, hepatic portal venous gas, and pneumoperitoneum. Barium enema examination is usually not necessary for diagnosis. Treatment consists of supportive measures, wide-spectrum antibiotics, and surgery (52 per cent of this series), with a combined mortality of 37 per cent. Long term sequelae are rare. The etiology is unknown. It is hypothesized that a primitive reflex redistribution of splanchnic blood flow, in response to significant infant stress, results in bowel ischemia with subsequent tissue damage and secondary bacterial invasion.