Background Despite its effectiveness in reducing mortality, colorectal cancer (CRC) screening rates are low, especially among low-income and minority groups; however, physician recommendation can increase screening rates. Methods We performed a multilevel analysis of the Medicare Current Beneficiary Survey data linked to Medicare claims and the Area Resource File to identify determinants of racial and socioeconomic disparities in CRC screening among 9985 Medicare Parts A and B beneficiaries with a usual physician. Recent CRC screening was defined as receipt of either a home fecal occult blood test, flexible sigmoidoscopy, or colonoscopy at recommended intervals. Results Unadjusted rates of screening were 48% for white and 39% for black beneficiaries (P<.001). Racial differences in CRC screening receipt were eliminated after adjustment for socioeconomic status as measured by income and education. Socioeconomic status disparities decreased but remained significant after adjustment for personal and health system factors. Awareness of CRC (adjusted odds ratio, 2.76; 95% confidence interval, 2.29-3.33) and having a primary care generalist (vs another specialist) as one's usual physician (adjusted odds ratio, 1.31; 95% confidence interval, 1.12-1.53) were associated with higher odds of screening, controlling for other factors. The odds of screening were also higher among those whose usual physician was rated more highly on information-giving skills. Conclusions Racial differences in CRC screening rates among Medicare beneficiaries with a usual physician are explained by differences in socioeconomic status. Beneficiaries with a primary care generalist as their usual physician had higher rates of CRC screening receipt. Increased efforts to make Medicare beneficiaries aware of the benefits of CRC screening may capitalize on the associations found in this study between CRC knowledge, physician information giving, and timely screening.