The presence or absence of pneumoperitoneum may not be as reliable an indicator of visceral perforation as commonly thought. Visceral perforation as commonly thought. Visceral perforation resulted in pneumoperitoneum in only 51 percent of patients in this study. Pneumoperitoneum occurred in 14 percent of patients in whom the extraalimentary intraperitoneal air had sources other than a perforated viscus. These patients' clinical findings were often indistinguishable from those of patients with a perforated viscus, and three patients underwent celiotomy unnecessarily. The routine use of the left lateral decubitus film to detect pneumoperitoneum and the judicious use of gastrointestinal contrast studies should be part of the optimal management of patients with suspected visceral perforation.