Objective: Idiopathic Granulomatous Mastitis (IGM) is a rare disease that is difficult to diagnose by only radiological methods and clinical findings. Method: First case; a 30 years old woman with a well circumscribed mass of 5 cm diameter at right breast applied to our hospital general surgery outpatient clinic. In the examination of fine needle aspiration biopsy (FNAB), palisaded epitheloid histiocytes and scattered atypical cells have been seen on a bloody and inflammatory background. We suggested excisional biopsy. Second case; a 39 years old woman applied to our hospital general surgery outpatient clinic with a sore mass in her left breast. The mass has been excised for malignancy suspect. Foci of abscesses, active chronical inflammation, areas of hemorrhage and numerous granulomas containing epitheloid histiocytes are observed microscopically. Results: In microscobic evaluation of the excisional biopsy of the first case prediagnosed as granulomatous mastitis invasive ductal carcinoma has been our diagnosis. In the second case there have been numerous granulomas containing epitheloid histiocytes, microscopically. Our diagnosis was Granulomatous mastitis in this patient prediagnosed as malignancy.