Objective: We examined the effect of Medicare's expansion of colorectal cancer (CRC) screening test reimbursement on racial/ethnic disparities in CRC screening. Methods: CRC screening was ascertained for Medicare beneficiaries (n = 30,893), aged 70 to 89, who had no history of any tumor and resided in 16 Surveillance, Epidemiology and End Results regions of the United States from 1996 to 2005. CRC screening tests were identified in the 5% sample of Medicare claims. Age–gender-adjusted percentages and -adjusted odds of receiving any guideline-specific CRC screening [i.e., annual fecal occult blood test (FOBT), sigmoidoscopy every 5 years or colonoscopy every 10 years] by race/ethnicity and Medicare coverage expansion period (i.e., prior to FOBT coverage, FOBT coverage only, and post–colonoscopy coverage) were reported. Results: CRC screening increased as Medicare coverage expanded for white and black Medicare beneficiaries. However, blacks were less likely than whites to receive screening prior to FOBT coverage (OR = 0.74, 95% CI: 0.61–0.90), during FOBT coverage only (OR = 0.66, 95% CI: 0.52–0.83) and after colonoscopy coverage (OR = 0.80, 95% CI: 0.68–0.95). Hispanics were less likely to receive screening after colonoscopy coverage (OR = 0.73, 95% CI: 0.54–0.99). Conclusions: Despite the expansion of Medicare coverage for CRC screening tests, racial/ethnic differences in CRC screening persisted over time in this universally insured population, especially for blacks and Hispanics. Future studies should explore other factors beyond health insurance that may contribute to screening disparities in this and younger populations. Impact: Although CRC screening rates increased over time, they were still low according to recommendations. More effort is needed to increase CRC screening among all Medicare beneficiaries. Cancer Epidemiol Biomarkers Prev; 20(5); 811–7. ©2011 AACR.