Objective[|]he main objective of this study was to analyze the differences in ipsilateral and contralateral internal mammary artery (IMA) and lateral thoracic artery (LTA) width in patients with malignant and benign breast tumor.[¤]Materials and Methods[|]A total of 104 female patients, of which 41 had benign and 63 had malignant tumors, were included in the study. The diameters of the IMA and LTA were measured from the widest point in T1-weighted post-contrast images. Breast magnetic resonance images were evaluated by a breast radiologist.[¤]Results[|]The ipsilateral IMA diameter of cases in the malignant group was found to be statistically significantly higher when compared with the benign group. In the benign group, the ipsilateral IMA diameter being an average of 0.43±0.87 mm larger than the contralateral IMA diameter was found to be statistically significant, whereas in the malignant cases, the ipsilateral IMA diameter being an average of 0.78±1.08 mm larger than the contralateral IMA diameter was found to be statistically significant. Also, in benign cases, the ipsilateral LTA diameter being an average of 0.31±0.70 mm larger than the contralateral LTA diameter was found to be statistically significant, whereas in malignant cases, the ipsilateral LTA diameter being an average of 0.29±0.68 mm larger than the contralateral LTA diameter was found to be statistically significant.[¤]Conclusion[|]The IMA and LTA diameters in benign and malignant cases were found to be higher in comparison with contralateral breast, independent of the size of the lesion.[¤]