A 74-year-old woman presented with a painless breast mass. Mammography of both breasts showed a large, lobulated calcific dense mass in the upper quadrant of the left breast. A skeletal scan showed very intense concentration of activity in the primary breast tumor in the left breast. A left mastectomy and axillary dissection were performed. The predominant histologic type of the mass was of an osteosarcoma and the diagnosis of a primary osteogenic sarcoma of the breast was made. Primary osteogenic sarcoma of the breast is rare and represents less than 1% of all primary breast malignancies.