Limited studies have investigated racial/ethnic survival disparities for breast cancer defined by estrogen receptor (ER) and progesterone receptor (PR) status in a multiethnic population. Using multivariable Cox proportional hazards models, we assessed associations of race/ethnicity with ER/PR-specific breast cancer mortality in 10,366 California women diagnosed with breast cancer from 1993 to 2009. We evaluated joint associations of race/ethnicity, health care, sociodemographic, and lifestyle factors with mortality. Among women with ER/PR+ breast cancer, breast cancer-specific mortality was similar among Hispanic and Asian American women, but higher among African American women [HR, 1.31; 95% confidence interval (CI), 1.05-1.63] compared with non-Hispanic White (NHW) women. Breast cancer-specific mortality was modified by surgery type, hospital type, education, neighborhood socioeconomic status (SES), smoking history, and alcohol consumption. Among African American women, breast cancer-specific mortality was higher among those treated at nonaccredited hospitals (HR, 1.57; 95% CI, 1.21-2.04) and those from lower SES neighborhoods (HR, 1.48; 95% CI, 1.16-1.88) compared with NHW women without these characteristics. Breast cancer-specific mortality was higher among African American women with at least some college education (HR, 1.42; 95% CI, 1.11-1.82) compared with NHW women with similar education. For ER-/PR- disease, breast cancer-specific mortality did not differ by race/ethnicity and associations of race/ethnicity with breast cancer-specific mortality varied only by neighborhood SES among African American women. Racial/ethnic survival disparities are more striking for ER/PR+ than ER-/PR- breast cancer. Social determinants and lifestyle factors may explain some of the survival disparities for ER/PR+ breast cancer. Addressing these factors may help reduce the higher mortality of African American women with ER/PR+ breast cancer.