Background: Idiopathic granulomatous mastitis (IGM) is a rare form of nonlactational mastitis. Due to the small number of case series and consequently inadequate prospective studies, there is still no consensus on the optimal treatment of IGM. In this study, we aimed to compare the efficacy of intralesional steroid injection with concomitant topical steroids to systemic steroid therapy only in the treatment of noncomplicated IGM. Methods: Between June 2015 and April 2018, the patients' data was prospectively collected and analyzed retrospectively. The study included a total of 78 female patients diagnosed with IGM. Patients were divided into 2 groups: the local steroid treatment group (intralesional steroid injection with topical steroid administration; group 1, n = 46) and the peroral systemic steroid treatment group (group 2, n = 32). Response to the therapy, side effects, recurrence, the need for surgical treatment, and complication rates were compared. Results: Forty-three patients (93.5%) in group 1 achieved a partial or complete response compared to 23 patients (71.9%) in group 2 after 3 months; this difference was significant (p = 0.012). The recurrence rates were significantly lower in group 1 (8.7%) compared to group 2 (46.9%; p = 0.001), and the need for surgical treatment was significantly less in group 1 (2.2%) than in group 2 (9.4%; p = 0.001). While the complication rates were similar between groups, a higher rate of systemic side effects was observed in group 2. Conclusion: Based on the results of our study, combined steroid injection and topical steroid treatment in IGM is as effective as systemic steroid treatment. We suggest that this combination therapy of topical steroids and local steroid injection should be used as first-line therapy in patients with noncomplicated IGM.