Background: In 2004 the CALGB 9343 trial determined that omission of radiation therapy after lumpectomy in women ≥ 70 years with ER+ T1N0 breast cancer did not significantly impact outcome. This retrospective study aimed to determine trends in locoregional therapy practice in this cohort and to determine its impact on outcome. Methods: Using SEER registry we identified 27852 pts who were ≥ 70 years with pT1N0M0 ER+ breast cancer diagnosed between 1990 and 2005. A cutoff of 2005 was chosen to ensure a minimum of 5 years of follow up. Pts were divided into 3 groups based on locoregional therapy received: a) mastectomy, b) lumpectomy plus radiation, c) lumpectomy without radiation. Breast cancer specific survival (BCSS) was computed and Cox models were then fitted to evaluate the association between type of locoregional therapy and BCSS, adjusted for various pt and tumor characteristics. We expanded the cohort to include pts diagnosed until 2010 to look at practice trends in locoregional therapy. Results: 11533 (41.4%) pts had mastectomy, 13035 (56.8%) pts had lumpectomy plus radiation therapy and 3284 (11.8%) pts had lumpectomy alone. At a median follow-up of 92 months, 5- year BCSS was 97%, 98% and 97% among pts who had undergone mastectomy, lumpectomy plus radiation and lumpectomy alone, respectively (p < 0.0001). Compared to those who underwent mastectomy, there was no significant difference in breast cancer deaths among those who underwent lumpectomy plus radiation (HR 0.89, 95% CI 0.7-1.003, p = 0.056) or lumpectomy alone (HR 1.13, 95% CI 0.94-1.36, p = 0.18). Comparing 1990, 2005 and 2010, the proportion of pts undergoing mastectomy steadily decreased (74.2%, 27.4% and 25% respectively) while proportion undergoing lumpectomy plus radiation steadily increased (21.1%, 51.5% and 52.7% respectively) as did proportion undergoing lumpectomy alone (4.7%, 21.1% and 22.4% respectively). Conclusions: Omission of radiation therapy after lumpectomy in older women did not seem to significantly impact BCSS in this population based analysis. Although the use of lumpectomy without radiation increased over time, post-lumpectomy radiation is still the more favored treatment practice.