Objective: We aimed to evaluate radiation-induced dermal side effects in patients with breast cancer who received radiotherapy by using HRUS. Materials and methods: Fifty-eight patients with breast cancer who had undergone radiation therapy after either total or partial mastectomy between June 2009-2012 were included in this study. All patients received radiotherapy in 25-28 fractions at 180-200 cGy doses to the peripheral lymphatics and breast and Thirty-one patients who had had partial mastectomies received doses of 10-16 Gy to the tumor bed. Skin thicknesses of mapped breast quadrants that were examined with HRUS using a high-frequency 13-18 MHz linear array transducer were measured starting at the end of the 6th radiotherapy month. The contralateral nonradiated breasts comprised the control group. Results: The ultrasonographic screening period after radiation therapy was a minimum of 6 months and a maximum of 36 months. The mean time was 14.4 ± 8.3 months for all patients. In the total mastectomy group, the skin thickness of the irradiated side and the control side was 1.0 ± 0.3 mm and 1.1 ± 0.3 mm (p>0.05). In the partial mastectomy group, the skin thickness of the irradiated side and the normal side was 1.3 ± 0.3 mm and 1.4 ± 0.3 mm (p>0.05). The mean skin thickness for patients who had grade 1 was 1.3 mm ± 0.2 mm, while for grade 2 it was 1.7 mm ± 0.7 mm. Conclusion: Evaluation of skin toxicity with HRUS is a noninvasive, inexpensive, and easily applied method. To decrease radiation-induced skin toxicity, new studies targeting contemporary radiotherapy techniques are necessary.