Pneumoperitoneum is not invariably associated with ruptured or perforated intra-abdominal viscus. To determine the incidence of free air associated with intra-abdominal viscus perforation, the medical records of 77 consecutive patients whose discharge or autopsy diagnosis included pneumoperitoneum or perforated viscus at a community hospital were retrospectively reviewed between June 1980 and October 1985. Abdominal viscus perforation, as determined by contrast studies or at operation, was not invariably associated with free air. Sixty-nine percent (23/33) of gastroduodenal, 30% (3/10) of small-bowel, and 37% (11/30) of large-bowel perforations had free air, as determined by preoperative x-ray film. Four cases with a total of six episodes of pneumoperitoneum were identified where viscus perforation was not documented. Pneumoperitoneum thus remains a reliable sign of viscus perforation; however, lack of this finding does not rule out perforation, and unusual causes must be considered.