This report is a retrospective evaluation of 12 case histories. All patients had been subjected to laparotomy on suspicion of acute appendicitis. The operative situations seemed to corroborate clinical expectations: an inflamed ileocecal process was assumed to be a result of performation of a gangrenous appendicitis. In three patients a primary adenocarcinoma arising from the appendiceal base was the incidental histologic finding postoperatively. In three other patients this inflammatory-looking process was related to a cecal carcinoma. In six patients a carcinoma existed unrecognized as the basic disease, these patients being subjected to intra-abdominal drainage only or in connection with appendectomy. In five instances a fecal fistula was the main persisting symptom of postoperative morbidity, in one patient even as long as two years after laparotomy. The problem in diagnostic verification of the initially unidentified carcinoma is illustrated. Attention is directed towards avoiding a false feeling of security in the presence of inflammatory manifestations in the right lower abdominal quadrant, which may misleadingly suggest a ruptured appendix.