Little evidence exists to guide adjuvant treatment decisions for women with breast cancer diagnosed after the age of 70.  With regard to adjuvant post-mastectomy radiation (PMRT), prior trials excluded women over the age of 70.  In our large, retrospective cohort study, we found that women over the age of 70 with high-risk breast cancer, defined as stage T3/4 or N2/3, derived a significant survival benefit from PMRT.  At five years follow up, overall survival was improved by 6% for high-risk patients who received PMRT.  This result is consistent with prior literature that has demonstrated a survival benefit for younger women with high-risk breast cancer who receive PMRT.  However, it is important to remember that our study was retrospective and not randomized, and is therefore subject to treatment assignment bias.  Ideally, randomized trials are needed to define optimal adjuvant treatment for older women with breast cancer.