Metastasis to the breast from extramammary malignancies is rare, but its recognition is important because the prognosis and treatment differ from that of primary breast cancer. We report a case of ovarian cancer with metastasis to the breast, which was found at the time of presentation. A 57-year-old woman presented with shortness of breath and was found to have a malignant pleural effusion. A right breast nodule contained papillary adenocarcinoma. Laparotomy showed bilateral ovarian papillary cystadenocarcinoma with dissemination in the peritoneal cavity. DNA image analysis showed multiple aneuploid stem lines. Immunohistochemical staining was positive with ovarian tumor marker OC125 but negative with breast tumor marker gross cystic disease fluid protein-15 (GCDFP-15) and estrogen receptor. The breast specimen was positive with OV632, a more specific tumor marker for ovarian cancer, thus favoring the ovary as the site of the primary tumor.