Appendicoliths cause acute appendicitis and appendicular perforation. Do appendicoliths cause acute abdominal pain in the absence of acute appendicitis? A retrospective observational study was undertaken of histology reports of all appendicectomy specimens from children < 16 years of age between January 1995 and December 2001. Specimens were categorised as perforated or uncomplicated acute appendicitis, non-inflamed, and "incidental" (removed during abdominal surgery for other indications). The presence of an appendicolith was noted. Clinical details were supplemented by selected case note review. Specimens in which the diagnosis of appendicitis or the presence of an appendicolith were not clearly defined (n = 20) were reviewed by an experienced, independent pathologist. 601 consecutive appendicectomy reports were analysed. The mean age of the study population was 9 years (range 1 day - 15.9 years) and there were 357 boys. An appendicolith was identified in 31/118 (26%) cases of perforated appendicitis, 60/352 (17%) cases of uncomplicated appendicitis, 12/59 (20%) cases of non-inflamed appendices, and only 1/72 (1%) cases of incidental appendicectomies. All patients with an appendicolith in the non-inflamed appendix group had presented with acute abdominal pain mimicking acute appendicitis. The frequency of an appendicolith in perforated appendicitis was significantly greater than in uncomplicated acute appendicitis (chi (2) = 4.8, 1 df, p < 0.05). There was no significant difference in the frequency of an appendicolith between non-inflamed appendices and acute appendicitis (either perforated or intact). Appendicoliths were rarely found in incidental appendicectomies, but these patients were younger. The frequency of appendicoliths in non-inflamed appendices was much greater than that expected from published autopsy data. Appendicoliths may cause acute abdominal pain that mimics acute appendicitis.