Background: Almost 60% of breast cancer in the U.S. occur in women aged >65, but these women are less likely to receive guideline-concordant care. Given existing treatment disparities by race/ethnicity, older minority women may be especially prone to potential gaps in breast cancer care. Hospitals serving higher proportions of minority patients are at risk to deliver suboptimal care, but how site of care impacts aging patients with breast cancer is not well defined. We sought to evaluate the association between race/ethnicity and breast cancer treatment delays in older women treated at minority-serving hospitals (MSH) vs non-MSHs. Methods: Women >65 years old with non-metastatic breast cancer diagnosed from 2010-2017 were identified in the National Cancer Database using data from Commission on Cancer (CoC)-accredited hospitals. Treatment delay was defined as >90 days from diagnosis to first treatment (surgery, chemotherapy, endocrine therapy). MSHs were defined as the top decile of hospitals serving predominantly Black or Hispanic patients. Multivariable logistic regression models adjusted for patient, disease, and hospital characteristics were used to determine the odds of treatment delay for women at MSHs vs non-MSHs across racial/ethnic groups. Results: 529,128 women (84.5% non-Hispanic White, 3.3% Hispanic White, 9.6% non-Hispanic Black, 0.1% Hispanic Black, 0.2% Native American, 2.5% Asian/Pacific Islander) were identified among 41 MSHs and 1,146 non-MSHs. Overall, time to treatment was <90 days in >95% of women (mean 33.4 days; standard deviation 26.4 days). Older women regardless of race at MSHs were more likely to suffer treatment delays than those at non-MSHs (odds ratio 1.31; 95% confidence interval 1.22-1.41). Compared to non-Hispanic White women, all minority groups had a higher likelihood of treatment delay regardless of MSH status (Table). Conclusions: Although most older women with non-metastatic breast cancer treated at CoC hospitals received care in a timely fashion, minorities and those treated at MSHs were more likely to experience treatment delays. Effective interventions addressing barriers to timely care at MSHs and among racial/ethnic minorities are needed.