Background: The NCCN guidelines state that breast RT may be omitted in patients > 70 years of age with ER+, clinically node-negative, T1 breast cancer (BC) who receive adjuvant ET. Available data on older patients notes that local relapses are the most frequent site of failure, and distant relapse rates are low. The side effects of ET are not inconsequential and negatively affect QOL. The objectives of this study are to examine clinical outcomes including overall survival (OS) in women ≥70 years of age treated by lumpectomy(L)+ET and L+RT in the NCDB. Methods: The 2004-2013 NCDB includes 76,431 women ≥70 years with ER+ stage I BC who underwent L, and had a minimum one year follow up. Women who received no adjuvant therapy, both ET+RT, or any chemotherapy were excluded. To limit the analysis to healthy women, we excluded subjects with a Charlson comorbidity index > 0. We identified 24,572 patients who received either adjuvant ET monotherapy or adjuvant RT alone. Among these, 46% (11,313) received ET and 54% (13,259) breast RT. Overall median follow up was 57 months (range: 12-143 months). Analysis of OS between the 2 treatment groups was performed using Kaplan-Meier statistics and Cox proportional hazards regression; propensity weighting was used to balance covariates across the 2 treatment groups. Results: After propensity weighting, demographic covariates including age, race, insurance, and facility type were balanced between the 2 treatment groups. The median OS for ET was 125.9 months (95% CI 120.1-131.8), and 127.2 months for RT (95% CI 124.5-131.7) (p < 0.0001). The weighted hazard of death was 11.7% less in women receiving RT compared to ET (HR 0.883, 95% CI 0.834-0.936, p < 0.0001). Conclusions: To our knowledge, this is the first large study comparing RT and ET monotherapy in healthy older women with stage I, ER+ BC. The OS with RT alone is not inferior to ET alone, and in this study population is noted to be better. While this analysis has various limitations not dissimilar from other NCDB database studies, our observations are encouraging and warrant further research with prospective studies.