Granulomatous mastitis (GM) is a rare benign inflammatory breast disease that affects mostly women of childbearing age with a history of breastfeeding. The etiopathogenesis is still unknown; however, inflammation as the result of a reaction to trauma, metabolic or hormonal processes, autoimmunity, and an infection with Corynebacterium kroppenstedtii have all been implicated. Clinical findings are pain, mass, hyperemia, and inflammation. Because the clinical presentation can mimic infectious mastitis or inflammatory carcinoma, the disease course is often protracted. The diagnosis is made by histopathology. Biopsies show a granulomatous formation in combination with a localized infiltration of multi-nucleated giant cells, epithelioid histiocytes, and plasma cells. Ultrasound, mammography, and magnetic resonance imaging are not specific; however, ultrasound and mammography should be done to exclude other pathologies. Due to the lack of data including randomized controlled studies, the management of GM is controversial. In Western industrialized countries, most authors use a therapy regimen starting with antibiotics and corticosteroids, followed by continuous steroid therapy and surgery in patients with persisting symptoms. More data are needed to define the best therapy. The role of immunotherapy has not yet been ascertained. The implementation of a registry to collect more information on this rare disease is highly recommended.