Background: Randomized trials and registry data established that breast conservation with lumpectomy (Lump) and breast radiotherapy (RT) yields equivalent cancer outcomes to mastectomy (Mast) for women with early stage breast cancer (BC). Clinical trial data since 2004 increasingly supports that Lump alone compared to Lump+breast RT results in equivalent survival and acceptable cancer control in women ≥ 70 years old with stage I (T1N0) hormone-sensitive (HS) BC on endocrine therapy. Since Lump alone represents sufficient treatment for elderly women with stage I HS BC we hypothesize that Mast rates have decreased in this subgroup. Methods: We used the Surveillance Epidemiology and End Results (SEER) registry data to conduct this study. We included women ≥ 70 years old with T1N0 HS BC classified as ER+ or PR+ from 2000-2012. We compared rates of Mast and Lump (+/-RT) in women diagnosed before 2004 to those diagnosed from 2005-2012. We also examined Lump and Mast rates by race: White, Black, and Asian-Pacific-Islander(API). Statistical analyses were performed using differences in proportions (p < 0.05 considered statistically significant). Results: 87,009 women met the inclusion criteria (N = 30,050 before 2004; N = 56,959 from 2005-2012). Since 2004, Mast rates decreased by 5.2% (95% CI, 4.5%-5.9%) from 32.6% to 27.4% (p < 0.0001). Lump rates increased by 3.4% (95% CI, 2.8%-4.1%) from 66.4% to 69.8% (p < 0.0001). Before 2004, elderly white women were more likely to undergo Lump compared to black (66.8% vs. 62.6%, p = 0.0421) or API women (66.8% vs. 61.6%, p < 0.0001) and less likely to undergo Mast compared to black (32.3% vs. 34.9%, p < 0.0001) or API (32.3% vs. 38.0%, p < 0.0001) women. Since 2004, elderly white women remained least likely to undergo Mast in comparison to black women (26.8% vs. 30.8%, p < 0.0001) or API women (26.8% vs. 33.6%, p < 0.0001). Conclusions: We found a modest decrease in Mast rates in elderly women with stage I HS BC since 2004. However, more than 25% of women in this subgroup continue to undergo Mast. Mast rates are higher in elderly black and API women compared to white women. Further study is warranted to understand why Mast rates did not decline more in this favorable risk population.