Background Idiopathic granulomatous mastitis is a rare inflammatory disease of the breast, for which there is a lack of consensus on the treatment protocol; it requires long-term follow-up and is associated with a high rate of relapse after surgical treatment. In this study, we report on the largest single-center cohort of idiopathic granulomatous mastitis treated with steroids + methotrexate. Methods We retrospectively examined the data of 33 patients histopathologically diagnosed with idiopathic granulomatous mastitis who were evaluated by our Rheumatology or General Surgery Clinics between 2013 and 2016. Results Of the 33 female patients (age: 38.64 ± 6.9 years), 24 were admitted with an initial diagnosis of idiopathic granulomatous mastitis, whereas 9 were admitted after surgical treatment. Remission was achieved in 87.9% of patients with steroid + methotrexate treatment, and there were no relapses during the 24-months follow-up period. Conclusions Steroid + methotrexate treatment is an effective and reliable method for ensuring long-term remission in patients with idiopathic granulomatous mastitis diagnosis.