Idiopathic granulomatous mastitis (IGM) is a chronic autoimmune inflammatory condition that can negatively affect patient psychology, that effective diagnostic protocols and treatment plans have not yet been established. Since the treatment protocols used differ, other causes of mastitis should be excluded. The purpose of this study was to compare ultrasonography (US) findings of IGM with type of the other mastitis (OM) to identify the imaging signs essential for a correct differential diagnosis.This retrospective study was approved by the University Ethics Committee. This study was between August 2017 and August 2018. Parenchymal distortion and no discrete mass, mass-like lesions with indistinct borders, tubular connections, duct ectasia-periductal thickening, skin thickening and presence of an abscess were evaluated in US for each breast lesion.The fifty-seven patients with IGM and 38 with OM were included in the study. The mean age was 35.2±8.4 and 43.6±12.5 years for those with IGM and OM, respectively. US showed tubular connections (43(75.4%)) with finger-like projections that tended to coalesce (P˂0.01) and mass-like hypoechoic lesions (51(89.5%)) with irregular margins in IGM. Most cases of OM, 37 (97.4%), had mass-like lesions with indistinct borders.The US findings of IGM sometimes overlap with types of OM. Although core biopsy is typically diagnostic, US findings are very useful in the differential diagnosis of IGM and OM. Especially, observation of tubular-related hypoechoic mass-like lesions may suggest IGM in the reproductive age patient with chronic mastitis.