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Objective: To compare and determine discriminative magnetic resonance imaging (MRI) findings of idiopathic granulomatous mastitis (IGM) and breast cancer (BC) that present as non-mass enhancement. Materials and Methods: This retrospective study includes 68 IGM and 75 BC cases that presented with non-mass enhancement on breast MRI. All patients with a previous history of breast surgery, radiotherapy, or chemotherapy due to BC or a previous history of mastitis were excluded. On MRI images, presence of architectural distortion skin thickening, edema, hyperintense ducts containing protein, dilated fat-containing ducts and axillary adenopathies were noted. Cysts with enhancing walls, lesion size, lesion location, fistulas, distribution, internal enhancement pattern and kinetic features of non-mass enhancement were recorded. Apparent diffusion coefficient (ADC) values were calculated. Pearson chi-square test, Fisher’s exact test, independent t test and Mann–Whitney U test were used as needed for statistical analysis and comparison. Multivariate logistic regression model was used to determine the independent predictors. Results: IGM patients were significantly younger than BC patients (<i>p</i> < 0.001). Cysts with thin (<i>p</i> < 0.05) or thick walls (<i>p</i> = 0.001), multiple cystic lesions, (<i>p</i> < 0.001), cystic lesions draining to the skin (<i>p</i> < 0.001), and skin fistulas (<i>p</i> < 0.05) were detected more often in IGM. Central (<i>p</i> < 0.05) and periareolar (<i>p</i> < 0.001) location and focal skin thickening (<i>p</i> < 0.05) were significantly more common in IGM. Architectural distortion (<i>p</i> = 0.001) and diffuse skin thickening (<i>p</i> < 0.05) were associated with BC. Multiple regional distribution was more common in IGM, whereas diffuse distribution and clumped enhancement were more common in BC (<i>p</i> < 0.05). In kinetic analysis, persistent enhancement was more common in IGM, whereas plateau and wash-out types were more common in BC (<i>p</i> < 0.001). Independent predictors for BC were age, diffuse skin thickening and kinetic curve types. There was no significant difference in the diffusion characteristics. Based on these findings, MRI had a sensitivity, specificity and accuracy of 88%, 67.65%, and 78.32%, respectively, in differentiating IGM from BC. Conclusions: In conclusion, for non-mass enhancement, MRI can rule out malignancy with a considerably high sensitivity; however, specificity is still low, as many IGM patients have overlapping findings. Final diagnosis should be complemented with histopathology whenever necessary.