Background: Whether timeliness of follow-up after abnormal mammography differs at facilities serving vulnerable populations, such as women with limited education or income, in rural areas, and racial/ethnic minorities is unknown. Methods: We examined receipt of diagnostic evaluation after abnormal mammography using 1998–2006 Breast Cancer Surveillance Consortium-linked Medicare claims. We compared whether time to recommended breast imaging or biopsy depended on whether women attended facilities serving vulnerable populations. We characterized a facility by the proportion of mammograms performed on women with limited education or income, in rural areas, or racial/ethnic minorities. Results: We analyzed 30,874 abnormal screening examinations recommended for follow-up imaging across 142 facilities and 10,049 abnormal diagnostic examinations recommended for biopsy across 114 facilities. Women at facilities serving populations with less education or more racial/ethnic minorities had lower rates of follow-up imaging (4%–5% difference, Pqqqlt;0.05), and women at facilities serving more rural and low-income populations had lower rates of biopsy (4%–5% difference, Pqqqlt;0.05). Women undergoing biopsy at facilities serving vulnerable populations had longer times until biopsy than those at facilities serving nonvulnerable populations (21.6 vs. 15.6 d; 95% confidence interval for mean difference 4.1–7.7). The proportion of women receiving recommended imaging within 11 months and biopsy within 3 months varied across facilities (interquartile range, 85.5%–96.5% for imaging and 79.4%–87.3% for biopsy). Conclusions: Among Medicare recipients, follow-up rates were slightly lower at facilities serving vulnerable populations, and among those women who returned for diagnostic evaluation, time to follow-up was slightly longer at facilities that served vulnerable population. Interventions should target variability in follow-up rates across facilities, and evaluate effectiveness particularly at facilities serving vulnerable populations.