Idiopathic spontaneous pneumoperitoneum is a rare condition we consider after exclusion of perforation of an intraabdominal viscus and other known causes of free intraperitoneal gas. We will report two cases of idiopathic spontaneous pneumoperitoneum seen during the year 1991 and discuss a rational way to get to the diagnosis. In the absence of peritoneal signs the rather unexpected amount of free intraperitoneal air is a constant finding. Reviewing the literature we found different opinions concerning the treatment of this condition. Regarding the benign character we emphasize a non-surgical management, given the careful exclusion of other, maybe fatal causes of pneumoperitoneum. Diagnostic peritoneal lavage may help to avoid unnecessary laparotomy.