A 58-year-old woman presenting with idiopathic granulomatous mastitis mimicking breast carcinoma is described. The mass was elastic, hard and painless, and located in the upper outer quadrant of the right breast. Fine needle aspiration cytology did not provide any diagnostic information. Mammography, ultrasonography and magnetic resonance imaging (MRI) strongly suggested malignancy. Excisional biopsy was performed for definitive diagnosis, and idiopathic granulomatous mastitis was demonstrated histopathologically. Neither wound complication nor recurrence has been identified in the patient, although corticosteroids were not used post operatively. We reviewed the literature, and found that our present case is rare in older patients, and that mammography, ultrasonography and MRI provide little information for differentiating between granulomatous mastitis and carcinoma.