Background: The aim of this study was to investigate the value of pre-treatment dynamic contrast-enhanced MRI (DCE-MRI) findings in predicting clinical and radiological response to treatment in patients with idiopathic granulomatous mastitis (IGM) receiving steroid therapy and to compare clinical and DCE-MRI results after treatment. Methods: Pre- and post-treatment MRI examinations of 86 patients (with a mean age of 33.8 years; range, 20–57 years) diagnosed with IGM between January 2014 and September 2022 were retrospectively evaluated. Lesion characteristics and longest diameter, number of involved quadrants, retroareolar involvement, and presence of fistula or lymphadenopathy were noted. Patients were categorized into clinical complete response (CCR), clinical non-response (CNR) groups based on clinical response and into radiological complete response (RCR) and radiological non-response (RNR) groups based on radiological response. Results: The analyses revealed no relationship between the lesion type (abscess, NME, abscess, and NME), presence of lymphadenopathy or fistula, number of involved quadrants, retroareolar involvement, and treatment response on pre-treatment MRI (p>0.05). The longest lesion diameter was smaller in the CCR group than in the CNR group (p = 0.02). After treatment, 40.7% (35/86) of the patients achieved RCR + CCR, while 16.3% (14/86) achieved RNR + CNR. On the other hand, 43% (37/86) of the patients achieved CCR + RNR. Conclusion: CCR is more common in patients with smaller lesions. Other pre-treatment MRI findings were not correlated with radiological or clinical response. A significant proportion of patients with CCR had residual lesions radiologically.