The coexistence of mucinous ovarian and appendiceal tumors in association with pseudomyxoma peritonei (PMP) is well established. However, there has been considerable debate regarding to the origin of the tumor in such cases. PMP was thought to originate from the ovary or peritoneal cavity. Based on clinicopathological, immunohistochemical, and molecular data, mucinous tumors involving the appendix and ovaries in women with PMP are clonal and derived from a single site, most likely the appendix. We report a case of a 73-year-old woman who had complained of lower abdominal distension. A magnetic resonance imaging of the abdomen and pelvis demonstrated a 21.8x10.0 cm cystic mass with thin enhancing septa arising from left ovary, and ascites. Additionally, tumor markers, cancer antigen-125 and carcinoembryonic antigen (CEA) were elevated to 196 U/ml and 14.5 ng/ml, respectively. On laparotomy the patient was found to have a ruptured huge right ovarian mass and amputed appnedix with mucus spillage. Subsequent surgical pathology results confirmed two separate malignant processes: borderline mucinous tumor and low-grade appendiceal mucinous neoplasm, ruptured. Immunohistochemical examination was performed on the surgical specimens. The appendiceal tumor stained negative for CK-7 and positive for CK-20, whereas the ovarian sample stained positive for CK-7 and negative for CK-20, consistent with malignant processes of independent origins. Key words: pseudomyxoma peritonei, mucocele, mucinous ovarian tumor.