Acute appendicitis is still a difficult diagnosis to make. Reports place the rate of incorrect diagnosis--the rate of negative laparotomy--at 15 to 42 per cent. This study is a prospective analysis of barium enema (BE) examinations performed upon 101 patients who presented with a history accompanied by signs and symptoms suggestive of, but not clearly diagnostic of, acute appendicitis. The over-all accuracy rate was 91.5 per cent. Sensitivity and specificity rates were 83 and 96 per cent, respectively. BE had a positive predictive value of 88 per cent and a negative predictive value of 95 per cent in this study. No complications resulted from the use of BE in this study, which included three instances of perforated appendicitis. We conclude that emergent BE is an inexpensive, safe and readily available adjunct to the diagnosis of acute appendicitis. Its use in the presence of a clear-cut presentation of acute appendicitis is not necessary. When clinical data were equivocal, BE reduced the rate of negative laparotomy to 7.2 per cent.