Idiopathic granulomatous mastitis (IGM) is an uncommon chronic inflammatory lesion of the breast with an uncertain optimal treatment regimen, the physical examination, and radiologic features of which may be confused with breast carcinoma. In this study, we aimed to describe the clinicopathologic characteristics of 33 patients who admitted to our breast policlinic and took the diagnosis of granulomatous (idiopathic and non-idiopathic) mastitis, and report the place of corticosteroids and the timing of surgery in the treatment of patients with IGM. The clinical features of 33 patients who presented to our breast policlinic with the complaint of breast mass and reached the final diagnosis of GM between March 2005 and October 2009 were reported. The most common symptoms were mass (n: 27) and pain (n: 11). Ultrasonography (USG) and biopsy were performed in all of the patients. Mammography (MMG) was performed in 9, and magnetic resonance imaging (MRI) in 10 patients. The diagnosis of idiopathic lobular granulomatous mastitis (ILGM) was made in 25 patients and tuberculous mastitis (non-idiopathic GM) in the remaining 8 patients. Twenty-four patients received steroid treatment except one who was pregnant. After giving birth, she also received steroids. One of the patients who developed recurrence after 11 months repeated the steroid therapy. Eight patients with tuberculous mastitis were placed on a regimen of antituberculosis therapy for 6 months. In the diagnosis of IGM, physical examination, USG, MMG, and even MRI alone may sometimes not be enough. They should be discussed altogether and the treatment should begin after definitive histopathologic result. Fine needle aspiration biopsy for cytology will result in a high level of diagnostic accuracy, however, core biopsy will reinforce the exact result. Corticosteroid therapy has been shown to be efficacious for IGM, but in the existence of complications such as abscess formation, fistulae, and persistent wound infection, surgical treatment has been the first method of choice.