Idiopathic granulomatous mastitis (IGM) is an uncommon breast disease often mistaken for breast infection or abscess. We present a case of IGM diagnosed after prolonged ineffective treatment of presumed infectious mastitis with abscess. Once the diagnosis was made with biopsy and further evaluation to exclude other causes of granulomatous disease, sinus tract debridement and closure by secondary intent resulted in resolution of symptoms in our patient. Many cases of IGM require immunosuppression with steroids, methotrexate or extensive surgery. To prevent morbidity, IGM should be considered in the differential diagnosis when presumed infectious mastitis with breast abscess does not respond to usual treatment.