This study was done to determine the association between appendiceal fecaliths or appendiceal calculi and the presence of acute appendicitis. We retrospectively reviewed the medical records of all patients from 1977 through 1986 who underwent appendectomy for a clinical diagnosis of acute appendicitis (group 1, 2,331 patients) or who underwent appendectomy either incidentally or during colectomy for nonappendiceal pathologic factors (group 2, 1,066 patients). Fecaliths were six times more common than calculi, but calculi were more often associated with perforated appendicitis or periappendiceal abscess (45 per cent) than were fecaliths (19 per cent). Appendiceal fecaliths and calculi appear to play a role in the pathogenesis of acute appendicitis and are associated with complicated appendicitis (perforation and abscess). Appendectomy should be considered for patients in whom an appendiceal calculus is recognized incidentally.