Endocrine therapy (ET) is the cornerstone of adjuvant therapy for hormone-receptor positive (HR+) breast cancer. The survival gap between African-American (AA) and white women with breast cancer is most pronounced in HR+ subtypes, and could be related to differences in ET use. The relationship between race and initiation of ET is not well defined. We investigated patterns of ET initiation by race in a diverse cohort of women covered by commercial health insurance. We identified 2,640 women with incident HR+ breast cancer in the North Carolina Central Cancer Registry whose records linked to commercial insurance claims using the Integrated Cancer Information and Surveillance System (ICISS) database. The sample included women age <65 years diagnosed with stage I-III HR+ cancers between 2004 and 2009. We used multivariate Poisson regression to examine the effect of race on likelihood of initiating ET. 14 % of women did not initiate ET within 12 months of diagnosis. AA women were 17 % less likely to initiate ET than whites (aRR 0.83, 95 % CI 0.74-0.93). When analyzed by subset, racial disparities persisted among women who received chemotherapy (aHR 0.67, 95 % CI 0.56-0.80) but not among women who did not receive chemotherapy (aHR 0.96, 95 % CI 0.76-1.21). AA women in our sample were less likely to initiate ET than whites, and this disparity was concentrated among chemotherapy-treated women. ET under-utilization may contribute to the racial survival gap in HR+ breast cancer, and represents an opportunity for intervention to reduce breast cancer disparities.