The frequency of biopsies with different types of mastitis among all patients with benign breast diseases in twenty years was 3%. About 2/3 of the patients were younger than 50 years, the average age was 46.7 years. Comparing the frequency of the different types of mastitis the puerperal mastitis is very rare in contrast to the increasing non-puerperal and granulomatous inflammatory breast lesions. The diagnosis "granulomatous mastitis" is one of exclusion. Both non-infectious and infectious causes must be considered. The origin of the granulomatous mastitis often is unknown, but it is supposed to be an autoimmune localized response due to the retained and extravasated fat and protein rich secretions in the ducts in cases of hyperprolactinemia (drug induced or by microprolactinomas) or hormonal imbalances characterized by epitheloid cell granulomas with giant cells microabscesses around lipid drops, but without necroses. An idiopathic type of granulomatous mastitis concerns young women in relationship to parturition with a similar histological pattern predominantly of the lobules. Special types of mastitis are the B-lymphocytic autoimmune mastitis associated with a longstanding insulin-dependent diabetes mellitus type I, the sarcoidosis, panniculitis and the rare but very different infectious diseases with breast involvement. Particularly in cases without features of secretory activity a carefully bacterioscopic and microbiologic work-up of fresh material from the surgical specimens is necessary for a final diagnostic report.