A case of secretory carcinoma of the breast in a 61-year-old woman is described. She came to our hospital complaining of a bloody nipple discharge. The physical examination revealed a 2.8 x 2.1-cm, firm, irregular lump with bloody nipple discharge in her left breast. Mammography demonstrated an irregular mass and ultrasonography showed an irregular hypoechoic mass accompanied with a cyst. Ductgraphy was done. It showed a dilated mammary duct leading to the cyst which was partially occupied with carcinoma. A cytologic smear of the nipple discharge and fine-needle aspiration cytology revealed similar findings, and both findings were malignant. A modified radical mastectomy was performed. A pathological examination revealed secretory carcinoma of the breast which had spread inward and outward from the cyst. In addition, the nipple discharge flowed from the cyst through the dilated mammary duct. The patient is presently alive and well 2 years after the operation. Secretory carcinoma is an extremely rare tumor of the breast and 48 cases have been reported in Japan. The present case is the first known case of secretory carcinoma demonstrating a bloody nipple discharge to come from a cyst which has been invaded by carcinoma.