Carcinoma of the breast is the most common malignancy in women in the United States. More than 40% of patients with human immunodeficiency virus (HIV) infection develop cancer during their illness, but breast cancer has seldom been reported. Twenty patients with breast cancer and HIV infection seen at the University of Miami/Jackson Memorial Hospital between January 1988 and August 2000 were retrospectively analyzed. Seventeen patients had a previous or concurrent diagnosis of HIV at the time of the breast cancer diagnosis. Their CD4 count ranged from 13-1126/microL (median, 309/microL). Most patients were premenopausal (16 of 20), with ages ranging from 31-61 years (median, 44 years). All stages of breast cancer were seen: ductal carcinoma in situ (2 patients), stage I (1 patient), stage II (9 patients), stage III (6 patients), and stage IV (2 patients). Ten tumors had estrogen receptors. Four of the 13 patients who underwent axillary lymph node dissection had abnormal lymph node findings, including 2 with follicular hyperplasia and 2 with caseating granulomas. Seven patients received chemotherapy with very poor tolerance. Estrogen receptor-positive patients were treated with tamoxifen. Of the 18 patients who presented with local disease, 7 have died: 2 of breast cancer, 4 of acquired immunodeficiency syndrome, and 1 of cardiac arrest. Nine patients remain free of disease (5 of them > 5 years) and 2 patients are alive with metastatic disease. Breast cancer in the HIV-positive population is similar to that seen in seronegative women. Most of the patients that are long-term survivors were treated with surgery and tamoxifen. The benefits of adjuvant chemotherapy are not clear.