Subdiaphragmatic free-air may be indicative of a perforated viscus; however, it is normally present after open abdominal surgery. The objective of this study was to determine the significance and incidence of subdiaphragmatic free air following laparoscopic cholecystectomy (LC). Cases of intestinal perforation following laparoscopic cholecystectomy from 1991 to 1995 at The University of Texas Health Science Center at San Antonio were reviewed and their association with subdiaphragmatic free air was determined. Twenty-five patients undergoing LC and 20 patients undergoing open cholecystectomy (OC) were prospectively evaluated with chest radiographs to determine the incidence and quantity of nonpathologic postoperative free air. Four cases of intestinal perforation resulting from trocar injuries or electrocautery burns occurred among 1603 LCs during this study period, for an incidence of 0.2 per cent. Three of the four patients with perforations were diagnosed postoperatively (2-5 days), and two patients had a moderate volume of subdiaphragmatic free air that aided the diagnosis. The incidence of subdiaphragmatic air following LC was 24 per cent, compared to 60 per cent for OC (P < 0.05). Eighty-three per cent of patients with retained air after LC had a minimal volume, compared to 67 per cent of patients after OC (P < 0.05). Nonpathologic subdiaphragmatic free air may normally be present following laparoscopic cholecystectomy but is uncommon 24 hours after the operation. When present, only a small volume is usually detectable. In the rare situation of intestinal perforation resulting from LC, subdiaphragmatic free air may be an important diagnostic finding.