We report on three cases of amyloidosis of the breast, two of which coincided with breast cancer. Patient no. 1, a 60-year-old woman, presented with two mass lesions measuring 2 cm in diameter, one in each breast. Histologically, a tubulo-lobular carcinoma was found in the left breast accompanied by vascular, interstitial, and periductal amyloid deposits; the lesion in the right breast consisted of amyloid deposits only. Patient no. 2, an 86-year-old woman, presented with an ulcerated breast tumor measuring 5 cm in diameter on the left side. A poorly differentiated invasive ductal carcinoma was found in the mastectomy specimen, and it coincided with interstitial and vascular amyloid deposits. In both patients, tumor cells had invaded the amyloid deposits. Patient no. 3, a 73-year-old woman, presented with a mass measuring 5 x 3 x 3 cm in her left breast. Fibrocystic changes, as well as interstitial and periductal amyloid deposits, were found histologically. In each case electron microscopy showed rigid, non-branching fibrils of indefinite length and measuring 10-12 nm in diameter; these were consistent with amyloid fibrils. Clinical data, immunohistochemistry, and/or amino acid sequencing of the fibril proteins extracted from formalin-fixed and paraffin-embedded tissue specimens provided evidence that the amyloid deposits were of immunoglobulin light chain origin in all three cases. A review of the literature revealed that kappa-light chain has been described more frequently than lambda-light chain in the breast and that there are no specific clinical or radiological symptoms of amyloidosis affecting the breast; a diagnosis can be achieved only by histology.