In a two-year period, 222 newborn infants were treated with ventilatory assistance, mainly for severe idiopathic respiratory distress syndrome (IRDS). Nine of these infants had roentgenographic evidence of pneumoperitoneum, four of them in the absence of gastrointestinal perforation. The presence of pulmonary air leaks (pulmonary interstitial emphysema, pneumomediastinum, pneumothorax) correlated poorly with the presence or absence of perforation. Abdominal roentgenograms of the patient in the upright position demonstrated intraperitoneal air-fluid levels in a patient with perforation and peritonitis; such air-fluid levels were absent when pulmonary air leak was the cause of pneumoperitoneum. Water-soluble contrast medium positively identified an ileal perforation in one patient.