Idiopathic chronic granulomatous mastitis is a rare disease in women at the reproductive life with clinic, mammographic, echographic and cytological characteristics suggestive of breast cancer. We report a case of breast pathology in a 35 years old woman who had a sensitiveness and eritematous tumor localized in the left breast. With the diagnosis of "mastitis", she was treated with antibiotics and corticoids for two weeks. Because the lesion and the sensitiveness persist and the mammographic and ecographic controls were suggestive of malignancy, the tumor was surgically removing. The histopathological diagnosis was idiopatic chronic granulomatous mastitis.