Granulomatous mastitis is a chronic benign inflammatory disorder of the breast which is extremely rare in male patients, and the prognosis is not well known mainly due to the limited number of cases reported in the literature.A 76-year -old male patient applied with nipple discharge and a palpable painless lump on his right breast for one month. Breast ultrasonography showed a 19x11 mm sized mass with solid hypoechoic components, and irregular shape. A presumptive diagnosis of breast carcinoma was made due to the results of imaging methods and the core biopsy, which resulted in unclearly. Simple mastectomy and sentinel lymph node biopsy was performed. The patient was discharged uneventfully on the second postoperative day. The histopathological findings supported the diagnosis of idiopathic granulomatosis mastitis.Male granulomatous mastitis, which previously reported in the literature, has unclear pathogenesis. It will be necessary to accumulate more case reports about GM in order to define the risk factors and optimizing the treatment.