OBJECTIVES: To assess whether greater colonoscopy use among white as compared with nonwhite Medicare enrollees since Medicare established coverage for colorectal cancer (CRC) screening has been associated with a widening in white versus nonwhite disparities in up-to-date CRC testing status. DESIGN: Serial cross-sectional analysis of Medicare claims. SETTING: Surveillance, Epidemiology, and End Results (SEER) regions in nine states, representing 14% of the U.S. population. PARTICIPANTS: A 5% random sample of fee-for-service Medicare enrollees aged 70 to 79 within each 6-month period from mid-1995 through 2003. MEASUREMENTS: Trends in up-to-date status (having a fecal occult blood test (FOBT) claim in the prior year or a sigmoidoscopy or colonoscopy claim in the prior 5 years) according to race or ethnicity, estimated using repeated-measures logistic regression adjusting for age, sex, rural versus urban residence, income, comorbidity, and SEER region. RESULTS: From mid-1995 through 2003, the adjusted percentage of enrollees that were up-to-date increased by a similar magnitude in whites (from 39.4% to 47.3%), blacks (from 29.0% to 38.1%), Asians and Pacific Islanders (from 33.1% to 41.8%), and Hispanics (from 23.7% to 33.2%). Although white versus nonwhite disparities in up-to-date status via colonoscopy widened, this was counterbalanced by narrowing white versus nonwhite disparities in up-to-date status via FOBT and sigmoidoscopy. CONCLUSION: White versus nonwhite disparities in up-to-date CRC testing status in Medicare enrollees largely persisted through 2003.