A case of breast cancer with choriocarcinomatous features (BCCF) is reported. The patient was a 38-year-old Japanese female with a long history of schizophrenia. Her nursing staff noticed a palpable mass in her right breast, which showed rapid growth. Following cytopathologic confirmation of a malignant breast tumor, she underwent mastectomy with ipsilateral axillary lymph node dissection. Histologic examination revealed BCCF, which was positive for placental alkaline phosphatase and human chorionic gonadotropin (HCG) by immunohistochemistry. The serum HCG level was high. She died 7 months postoperatively, with multiple metastases of BCCF to the chest wall, lung and liver.