Abstract Background: Five-year breast cancer survival rates are lower among Hispanic and African-American women than among Non-Hispanic White women. Differences in breast cancer treatment likely play a role. Adjuvant hormonal therapies increase overall survival among women with hormone receptor-positive breast cancer. Methods: We examined racial/ethnic differences in use and duration of adjuvant hormonal therapy among 3,588 postmenopausal women enrolled in the Women's Health Initiative (WHI) Extension Study. Women diagnosed with hormone receptor-positive localized or regional stage breast cancer after study enrollment were surveyed between September 2009 and August 2010 and asked to recall prior use and duration of adjuvant hormonal breast cancer therapy. ORs comparing self-reported use and duration with race/ethnicity (Hispanic, African-American, Asian/Pacific Islander vs. Non-Hispanic White) were estimated using multivariable-adjusted logistic regression. Results: Of the 3,588 women diagnosed from 1994 to 2009; 3,039 (85%) reported any use of adjuvant hormonal therapy, and 67% of women reporting ever-use who were diagnosed before 2005 reported using adjuvant hormonal therapy for the optimal duration of 5 years or more. In adjusted analysis, no statistically significant differences in use or duration by race/ethnicity were observed. Conclusions: This study did not find significant differences in use or duration of use of adjuvant hormonal therapy by race/ethnicity. Impact: Findings should be confirmed in other population-based samples, and potential reasons for discontinuation of therapy across all racial/ethnic groups should be explored. Cancer Epidemiol Biomarkers Prev; 22(3); 365–73. ©2012 AACR.