Appendiceal tumors are rare, late diagnosed neoplasms that may not be differentiated from adnexal masses even by advanced imaging methods and other diagnostic procedures. They may be asymptomatic and remain undiagnosed until surgery. We report a case of an 80-year-old postmenopausal woman presenting with a pelvic mass and a history of weight loss. The patient underwent laparotomy which revealed an appendiceal mucocele, for which she received a full oncological procedure. The histology report showed a low-grade appendiceal mucinous neoplasm, and the patient underwent six cycles of chemotherapy. Appendiceal tumors should be kept in mind in patients with adnexal mass.