Carcinoma of the breast occurs so infrequently in men that it is not at al well known either to patients or physicians. The causes of breast cancer in men are unknown. The most common clinical manifestation of breast cancer in men is a painless, firm subareolar mass or a mass in the upper outer quadrant of the breast. Diagnosis can be confirmed by fine-needle aspiration or surgical biopsy. Infiltrating ductal carcinoma is the predominant histologic type. After primary surgical treatment, men with axillary lymph node metastasis should receive adjuvant systemic chemotherapy. The use of radiation therapy for local control of the disease is recommended if there is invasion of the chest wall. Because most men with carcinoma of the breast have estrogen and progesterone-receptor positive tumors, breast cancer in men is likely to respond to hormonal manipulation.