Acute appendicitis with its characteristic clinical course is one of the most common diagnoses that require urgent surgery. The following three case reports present patients with symptoms typical of acute appendicitis which was, however, not confirmed intraoperatively. Preoperative CT or MRI were not requested because symptoms clearly indicated acute appendicitis. The first case describes a male patient with right-sided diverticulitis, the second case report involves a pregnant woman in 33rd week of gestation with right adnexal torsion due to a dermoid cyst, and in the last report, a case of spontaneous perforation of appendiceal mucinous neoplasm is presented.Key words: right-sided diverticulitis - dermoid cyst - adnexal torsion - mucinous neoplasm - pseudomyxoma peritonei - appendicitis.