In 2003, a Committee of the Institute of Medicine of the National Academy of Sciences summarized hundreds of studies documenting that US racial minorities, especially African Americans, receive poorer quality health care for a wide variety of conditions than their White counterparts. These racial differences in health care persist after controlling for sociodemographic factors and patients' ability to pay for care. The Committee concluded that physicians' unconscious negative stereotypes of African Americans, and perhaps other people of color, likely contribute to these health care disparities. This paper selectively reviews studies published after 2003 on the likely contribution of physicians' unconscious bias to US health care disparities. All studies used the Implicit Association Test which quantifies the relative speed with which individuals associate positive attributes like "intelligent" with Whites compared to Blacks or Latino/as. In addition to assessing physicians' unconscious attitudes toward patients, some studies focused on the behavioral and affective dimensions of doctor-patient communication, such as physicians' "verbal dominance" and whether patients felt respected. Studies reviewed found a "pro-white" unconscious bias in physicians' attitudes toward and interactions with patients, though some evidence suggests that Black and female physicians may be less prone to such bias. Limited social contact between White physicians and racial/ethnic minorities outside of medical settings, plus severe time pressures physicians often face during encounters with patients who have complex health problems could heighten their susceptibility to unconscious bias.