Amyloid tumors of the breast are extremely rare. Few isolated cases have been reported to date. Amyloid involvement of the breast has no specific diagnostic features on mammography; on occasion, this causes diagnostic challenges. In this paper, the case of a 58-year-old woman with an amyloid tumor of the breast, which developed secondary to long-standing rheumatoid arthritis, is presented. She presented with a palpable mass in her right breast, which led to an erroneous clinical diagnosis of breast cancer. The unusual mammography findings are demonstrated and the differential diagnosis, in light of the radiological images and the clinical and pathologic features, is discussed.