OBJECTIVES: Although adjuvant endocrine therapy (AET) is becoming an important cornerstone of treatment in Medicare breast cancer survivors, few studies have examined variations in the use of this treatment by potentially important sociodemographic influences like patient race and geography. This research examined the influences of such variables on access and use of AET in Medicare breast cancer survivors enrolled in the Part D drug benefit program from 2007-2011. METHODS: We included 18,067 adult women who were diagnosed with stage I-III, hormone-receptor positive, primary breast cancer and who newly started adjuvant endocrine therapy after the primary treatment for breast cancer. Hot spot analysis was conducted to explore geographic variations in adjuvant endocrine therapy adherence. Geographically weighted logistic regression was used to examine whether the impacts of factors associated with adherence after initial breast cancer treatment varied across the region. RESULTS: A random effects multivariate logistic regression analysis adjusting for contextual SES, health professional shortage treatment, and tumor characteristics between racial/urban status and 1st year use of AET retained significant differences in racial effects ( African American [AA] vs white OR = 0.80, 95% CI 0.70-0.92; other minorities combined vs white OR = 1.25, 95 % CI 1.08-1.47); urban geography effect , however, remained significant (non-metropolitan vs metropolitan OR = 0.93, 95% CI 0.81-1.07). Multivariate logistic regression analysis using Medication Possession Ratios > .80 as outcome also retained bivariate differences (AA vs white OR = 0.99, 95%CI 0.88-1.11; Other minorities vs white OR = 1.39, 95%CI 1.22-1.58; non-metropolitan vs metropolitan OR = 1.04, 95%CI 0.93-1.15). CONCLUSIONS: Our analyses find significant variations in access and use of AET therapy with African American and rural patients less likely to have optimal use. Further research is needed to examine and eliminate sociodemographic disparity in access and use of life saving cancer treatments.