Preoperative diagnosis of appendiceal mucoceles is rare. If untreated, one type of mucoceles may rupture producing a potentially fatal entity known as pseudomyxoma peritonei. The importance of diagnosing appendiceal mucoceles is highlighted through a case presentation of a woman who had an incidental finding of mucinous cystadenoma of the appendix during colonoscopic evaluation for occult gastrointestinal bleeding. A detailed review of the medical literature regarding appendiceal mucoceles is presented, with emphasis on the pathologic, clinical, radiologic, and evolving endoscopic features. Surgical options and prognosis are discussed.