Radiation therapy is fundamental in the management of breast cancer patients treated with breast-conserving surgery. After whole breast irradiation, an additional boost dose is often applied to the primary tumor bed. While such practice has shown to improve local control, its benefit has never been analyzed in HER-2 positive patients treated with trastuzumab. Here, we analyze the effect of radiation therapy boost on local control in patients with HER-2 positive breast cancer. The HERA trial is a phase III prospective randomized clinical trial that established the efficacy of trastuzumab in HER-2 positive breast cancer. The current study is a retrospective analysis of 1082 patients treated with breast conservative surgery, radiation therapy and adjuvant trastuzumab. The primary endpoint of the study was to determine the effect of a radiation boost on local recurrence. Kaplan-Meier curves were generated, and hazard ratios were estimated using COX regression. Our analysis included 441 patients (40.8%) who received radiation therapy boost and 641 patients (59.2%) who did not. Patients from both groups had similar baseline characteristics in terms of age, nodal involvement, and grade. At a median follow up of 10 years, local control was 93% (CI: 90-95%) in the radiation boost group as compared to 91% (CI: 89-93%) in the no boost group (p = 0.33). When analyzing patients by age, no local control benefit for additional boost was noted in patients younger than 40 (p = 0.54) or older than 40 (p = 0.42). Furthermore, no local control benefit for boost was noted in both hormone receptor (HR) subtypes (HR +: p = 0.75; HR -: p = 0.10). HER-2 positive breast cancer patients treated with breast-conserving surgery, whole breast radiation and trastuzumab have excellent local control. Delivery of an additional radiation boost in this patient population was not shown to further improve local control in our study. Given the improvement in local control outcomes in the modern era, future studies are needed to identify subgroups of HER-2 positive patients who derive benefit from radiation boost.