Mucocele of the vermiform appendix is a rare disease of the appendix caused by mucoid substance retention in its lumen, due to obstruction or hyperproduction due to appendiceal retention cysts, mucosal hyperplasia, mucinous cystadenomas and cystadenocar­cinomas. Therefore, also appendiceal malignancy can be the underlying cause, making accurate preoperative diagnosis imperative, even if this disease is often asymptomatic and an early diagnosis still remains very difficult on imaging studies. In women, appendiceal mucoceles can sometimes present on clinical and instrumental findings as a right adnexal mass mimicking an ovarian neo­plasm. A rare case of appendiceal mucocele in a 36-year-old women with a right-sided painful pelvic mass is presented. The mucocele was misdiagnosed as a cystic complex mass of the right adnexa both clinically and ultrasonographically. Serum levels of CEA and CA19-9 were increased. Explorative laparoscopy was performed revealing an enlarged vermiform appendix with the uterus and adnexa macroscopically normal, and no signs of intraperitoneal metastasis or adnexal torsion. Laparotomic appendectomy followed. Histological examination revealed a mucinous cystadenoma of the vermiform appendix. This clinical entity of appendiceal mucocele should always be considered by gynaecologists as well as gastroenterologists in the differential diagnosis of patients presenting a right-sided adnexal mass on ultrasound in order to choose the best surgical approach.