Appendiceal mucocele is a rare disease (0.3% of all appendectomy) and is characterized by the accumulation of mucoid material in the appendiceal lumen. Etiopathogenesis can be inflammatory or neoplastic. Four entities can be distinguished on the basis of histopathologic epithelial characteristics: simple appendiceal mucocele (AM), mucocele with epithelial hyperplasia, cystadenoma and cystadenocarcinoma; the last two subgroups represent neoplastic forms. Dissemination of neoplastic cells and mucoid material in abdominal cavity, caused by appendiceal perforation, clinically results in pseudomyxoma peritonei which is the dramatic evolution in 10-15% of cases. Clinically it can remain either asymptomatic for long time or it can manifest with abdominal pain that can be associated with the presence of a palpable mass. The most common clinical manifestation is pain in the right iliac fossa. Preoperative diagnosis is rare, while it is more frequently intraoperative. Therapy is fundamentally surgical: appendectomy is curative for simple AM, for AM with epithelial hyperplasia and for cystadenoma with intact appendiceal base; cecum resection is indicated for cystadenoma with larger base of implantation; right hemicolectomy has been the elective treatment in case of cystadenocarcinoma for several years although Gonzalez-Moreno and Sugarbaker have recently demonstrated its validity as definitive treatment only if it is performed in order to obtain complete cytoreduction, if there is lymph node involvement, or if histopathological examination indicates non-mucinous type. We report the case of a 60-year-old woman that presented with cystic neoformation in the right iliac fossa, that was preoperatively considered deriving from the ovary. We intraoperatively found the presence of appendiceal mucocele that histological examination defined as mucinous cystadenoma.