Breast cancer in men is rare and most often occurs at or after the age of 60 years. Prognosis is poor when it is discovered at a late stage, as it often is in men, although it should be easier to detect because men have so little breast tissue. The causal mechanism appears to depend on hormone metabolism abnormalities related to elevated estrogen or prolactin levels. A family history of breast cancer is found in 5-10% of cases. Infiltrating ductal carcinoma accounts for most cases (70-90%) of male breast cancers. In situ but not invasive carcinoma is exclusively ductal and accounts for 7% of cases. Spread to lymph nodes is observed in 50-75% of cases. Immunohistochemical analysis shows that tumors are positive for progesterone and estrogen receptors more frequently in men than women. Diagnosis is based on clinical examination, ultrasonography, and mammography. Aspiration cytology often makes it possible to confirm the malignancy. Excisional biopsy with an immediate intraoperative pathology examination confirms malignancy and makes wider excision possible during the same procedure. A modified radical mastectomy with removal of some lymph nodes (Patey's mastectomy) is the standard basic treatment. Locoregional radiotherapy is very often indicated. Hormone therapy is also a first-line treatment. Chemotherapy is reserved for young men with substantial lymph node invasion and negative for hormonal receptors. The prognosis of breast cancer in men remains uncertain because of the frequently late diagnosis, unpredictable course, and high potential for metastasis.