Recent reports suggest that providers' implicit attitudes about race contribute to racial and ethnic health care disparities. However, little is known about physicians' implicit racial attitudes. This study measured implicit and explicit attitudes about race using the Race Attitude Implicit Association Test (IAT) for a large sample of test takers (N=404,277), including a sub-sample of medical doctors (MDs) (n=2,535). Medical doctors, like the entire sample, showed an implicit preference for White Americans relative to Black Americans. We examined these effects among White, African American, Hispanic, and Asian MDs and by physician gender. Strength of implicit bias exceeded self-report among all test takers except African American MDs. African American MDs, on average, did not show an implicit preference for either Blacks or Whites, and women showed less implicit bias than men. Future research should explore whether, and under what conditions, MDs' implicit attitudes about race affect the quality of medical care.