Objective: Ovarian malignancy is highly suspected when patients present with an ovarian cystic mass lesion accompanied with ascites. However, aside from the primary origin, a metastatic lesion should be considered, since the ovary is frequently metastasized from cancers of other organs, such as the genital tract, gastrointestinal tract, and breast. Herein, we report the case of a patient with a left adnexal mass and ascites to emphasize consideration of metastatic ovarian tumors from non-gynecologic organs. Case Report: A 47-year-old woman with a history of right breast infiltrating lobular carcinoma, T3N0M0, grade 3, was treated with modified radical mastectomy and axillary lymph-node dissection in July 2001. Tumor recurrence was noted in December 2003. Therefore, she underwent palliative radiotherapy and various kinds of chemotherapy. In March 2006, she experienced poor appetite and abdominal fullness, and was found to have a 12-cm adnexal mass accompanied with ascites. Ovarian cancer was suspected, and exploratory laparotomy was performed. However, metastatic carcinoma of the ovary of breast origin was finally diagnosed. Conclusion: In cases of pelvic tumors in patients who have a history of other primary cancers, metastasis should be suspected initially. Although the prognoses of these patients seem to be worse, intensive cytoreductive surgery would improve quality of life and offer a chance of better survival in highly selected patients.