Eight cases are reported of an unusual breast lesion consisting of dense intralobular, perilobular, and perivascular lymphocytic infiltrates associated with lobular atrophy and sclerosis. Immunologic studies on paraffin-embedded tissue (seven cases) and frozen tissue (two cases) demonstrated a predominance of B-cells and expression of HLA-DR antigen in involved lobular epithelium. The immunologic features of this lesion are reminiscent of lymphoepithelial lesions of salivary glands and other sites. A possible autoimmune pathogenesis is suggested.