The term mastopathy describes a variety of proliferative and regressive transformations of the mammary glandular tissue. The reason is always a hormonal dysfunction. The mastopathy is mostly an abnormal transmutation of the glandular tissue, rarely a neoformation of tissue. Usually both breasts are affected. The mastopathy is caused by dysfunctioning hormonal regulation, by which the estrogen-progesteron-balance is shifted towards estrogen. Estrogen causes proliferation of the glandular tissue. This can express itself as adenosis, hyalinosis, papillomatosis, or epitheliosis. Increased glandular secretion causes expansion of the excretory ducts and formation of cysts.