Postoperative pneumoperitoneum is a normal finding in the adult. References to free air left behind in the peritoneal cavity of these older patients following laparotomy (1, 2, 3) occur in the literature, but the authors have been unable to find any mention of this problem with specific reference to infants and children. It is generally agreed that air in the peritoneal cavity of an adult following laparotomy will persist for seven to fourteen days, and it has been reported as late as twenty-three days. It was in 1952 that the problem was first encountered in an infant by one of the authors. An eight-day-old male infant was transferred to the Children's Hospital of Philadelphia because of vomiting bloody, bile-stained fluid since birth. On admission, the baby was extremely dehydrated and almost dead. Roentgen examination of the abdomen (Fig. 1) revealed a mechanical obstruction of the small bowel, most probably in the ileum. Laparotomy confirmed the roentgen finding of obstruction due to an ileal atresia about 8 inches proximal to the ileocecal valve. Following resection and an end-to-side anastomosis, the baby did remarkably well, and it was thought that he would probably survive in spite of the long delay before treatment. On the fourth postoperative day the abdomen became somewhat distended, and roentgen examination (Fig. 2) revealed a rather severe degree of pneumoperitoneum. Considerable discussion ensued, and finally, on the basis of adult standards, it was decided not to operate. The following day the abdomen was even more distended, and roentgen examination revealed slightly more air in the peritoneal cavity. Laparotomy was again performed; a leak was found at the site of the anastomosis and a severe peritonitis was present. Death occurred five days later. Obviously the pneumoperitoneum was not a normal postoperative finding. Two years later, in 1954, a similar problem arose, and again observance of adult standards led to a mistake in diagnosis. A four-week-old female infant was admitted because of rapid enlargement of the head since birth. A diagnosis of a communicating hydrocephalus was made and a subarachnoid-peritoneal shunt was performed. Three days postoperatively the abdomen became distended. Roentgen examination revealed a pneumoperitoneum (Fig. 3, A). Again it was presumed that this free air represented the normal pneumoperitoneum expected in the adult following laparotomy. The following day the abdomen was even more distended. Roentgen examination (Fig. 3, B) showed about the same amount of free air in the abdomen, but now with fluid in the peritoneal cavity as well. At laparotomy a perforation was found in the small bowel. This defect was closed, and with supportive treatment the baby recovered.