Free intra-peritoneal gas--an unusual aetiology.

The presence of free gas under one or both hemidiaphragms on an erect chest x-ray is most frequently the result of recent abdominal surgery or, in the absence of such surgery, is almost always indicative of a perforated abdominal viscus. A case is reported of a patient in whom pneumoperitoneum was discovered incidentally on a chest x-ray following extensive pelvic manipulation for acute inversion of the uterus.