Gynaecomastia, the enlargement of the male breast, is considered as an andrological disease. To date, a review on male breast cancer (MBC) has not been published in an andrological journal. The papers underlying this review were published from authors of different institutions: Clinical Genetics, Dermatology, Gynaecology, Internal Medicine, Oncology, Pathology, Psychiatry, Radiology and Surgery. MBC accounts for approximately 1% of breast cancer patients. A total of 182 men died of breast cancer in 1999, in Germany. In the US, 1500 new cases per year occur. MBC accounts for <5% of surgically removed breast lumps. Diseases with increased oestrogen action increase the risk of MBC. Mutations of distinct genes are estimated to account for up to roughly 10% of MBC. BRCA1 and BRCA2 gene mutations are responsible for approximately 80% of the families with hereditary breast cancer. The diagnosis of MBC is not possible without histological examination. Different diagnostic procedures such as clinical diagnosis, sonography, mammography, fine-needle biopsy and core needle facilitate the decision whether a biopsy is necessary.