Infarction of a breast fibroadenoma usually occurs in young females during pregnancy or lactation. This report describes a rare case of the total infarction of a fibroadenoma in a 58 year old postmenopausal woman. The chief complaint was a rapidly enlarged, slightly painful lump. Medullary carcinoma was suspected on palpation and mammography. Microscopically, the tumor was composed of a coarsely lobulated necrotic mass invaginated into an epithelial lined cyst. This was interpreted as an infarcted intracanalicular fibroadenoma, although the possibility of an infarcted phyllodes tumor cannot be entirely excluded. The significance of this rare event is the possible confusion with carcinoma. Extensive search for viable tissue is essential for the confirmation of the diagnosis.