Although postoperative pneumoperitoneum is a common finding, it is particularly disturbing when there is an increase in the amount of postoperative pneumoperitoneum or when the radiographic finding of pneumoperitoneum is accompanied by such physical findings as increased abdominal tenderness, peritoneal signs or paralytic ileus. Four patients operated upon at the Mount Sinai Hospital are presented. All patients underwent abdominal surgery for treatment of some form of inflammatory bowel disease and all were receiving systemic corticosteroids in the postoperative period. Abdominal findings of tenderness, ileus and peritoneal irritation developed shortly after the removal of Penrose drains in the postoperative period. Pneumoperitoneum was confirmed by abdominal roentgenographs. The first patient in this group underwent a laparotomy with essentially negative findings other than a freely open drain tract. The subsequent three patients were managed by close observation and frequent abdominal radiographs. These three patients had contrast roentgenographic studies of the upper gastrointestinal tract to rule out perforation of a peptic ulcer, and in the patient upon whom reservoir ileostomy had been performed, a contrast study of the reservoir was performed. All patients recovered fully with this management and there were no sequelae. The mechanism for the appearance of pneumoperitoneum after removal of drains, particularly when the patient is receiving systemic corticosteroids, is discussed. Emphasis is placed on the need to consider and rule out perforation of a hollow viscus in this situation before accepting drain removal as the sole cause of post-operative pneumoperitoneum.