Breast pathology that is characteristic of patients infected with human immunodeficiency virus (HIV) has not been addressed in the literature. HIV may directly and indirectly affect the glandular, mesenchymal, and intramammary lymphoid tissue in seropositive patients. Likely infections in this setting include tuberculous mastitis and pyogenic abscesses that may lead to fatal septicemia. Benign stromal changes include gynecomastia, adipose tissue deposition as part of the fat maldistribution syndrome, and pseudoangiomatous stromal hyperplasia. Breast carcinoma in HIV-infected patients occurs at a relatively early age, with increased bilateral disease, unusual histology, and early metastatic spread with a poor outcome. However, the link between breast cancer and HIV remains controversial. Kaposi's sarcoma and non-Hodgkin's lymphoma may also be localized to the breast in patients with acquired immunodeficiency syndrome (AIDS). This article reviews benign and malignant breast diseases that are likely to be encountered in patients with HIV/AIDS.