Background: Re-excision for positive margin(s) following a lumpectomy for breast cancer is generally recommended. Whether radiation therapy can adequately address positive margins and thereby preclude a reoperation in elderly women with small breast cancer is not known. Methods: We evaluated a cohort of 71,607 women age ≥ 70 years with Stage I, ER+ breast cancer with lumpectomy and hormone therapy diagnosed between 1998 and 2012 in the National Cancer Data Base. Patients were divided into three groups: (1) positive margins (2) negative margins, and (3) positive margins with radiation therapy (RT). Clinicopathological and sociodemographic variables were compared among these groups. Univariate and multivariate analysis were employed, as was inverse propensity of treatment weighting (IPTW) methods to create both a weighted and unweighted analysis based on propensity score methods assigning probability of being treated. Results: The positive margin rate for the entire group was 1.81%. The 5-yr overall survival (OS) rates for the unweighted positive margins group, negative margins group, and positive margins + RT group were 57.75%, 83.81%, and 83.66%, respectively (P < 0.0001). The median survival time (months) was 76.16, 130.23, and 133.45, respectively. Significant predictors (P < 0.01) in both the unweighted and weighted analyses of OS include treatment groups, age, and comorbidities. Conclusions: Radiation therapy for positive surgical margins is a viable option for elderly women with small ER+ tumor treated with lumpectomy and hormonal therapy.