Appendiceal diverticula are uncommon lesions. A retrospective study of appendiceal diverticula was done for 1379 appendectomies is performed from June 1991 to May 1996. Thirty-six cases (2.6%) of appendiceal diverticula were found. Only one case was detected operatively; the rest of them were diagnosed pathologically. These thirty-six cases have been classified into three groups: 23 cases of primary appendiceal diverticulitis, 8 of secondary appendiceal diverticulitis, and 5 of simple diverticulosis. The clinical manifestations of primary appendiceal diverticulitis were different from those of typical acute appendicitis. Primary appendiceal diverticulitis was seen mainly after the fourth decade of life. The pain came on rather insidiously and seemed to extend over a longer period. A history of previous attack was frequent. The rate of perforation in primary appendiceal diverticulitis was 78.2%.The false form of appendiceal diverticula was more common in most series. Also, no case was detected in appendectomies performed on many patients under 10 years of age with a diagnosis of appendicitis. They seemed to develop after birth and were seen frequently along the mesenteric border. The rate of mucosal hyperplasia in appendiceal diverticula was 61.1%, higher than that for appendicitis. Vascular hiatus between muscular bundles along the mesenteric side, and the mesenteric covering over the diverticula, as well as the inability of false diverticula to endure high intraluminal pressures, seem to be pathophysiologically associated with the cause and the high perforation rate in appendiceal diverticula. The clinical picture and the pathologic findings of primary appendiceal diverticulitis are definitely different from those of acute appendicitis. We suggest primary appendiceal diverticulitis be regarded as a clinical entity, not a variant of acute appendicitis. The patient with atypical right lower quadrant pain should be examined with this diagnosis in mind.