OBJECTIVES: We sought to find racial differences in the effects of trust in the health care system on preventive health service use among older adults. METHODS: We conducted a telephone survey with 1681 Black and White older adults. Survey questions explored respondents' trust in physicians, medical research, and health information sources. We used logistic regression and controlled for covariates to assess effects of race and trust on the use of preventive health services. RESULTS: We identified 4 types of trust through factor analysis: trust in one's own personal physician, trust in the competence of physicians' care, and trust in formal and informal health information sources. Blacks had significantly less trust in their own physicians and greater trust in informal health information sources than did Whites. Greater trust in one's own physician was associated with utilization of routine checkups, prostate-specific antigen tests, and mammograms, but not with flu shots. Greater trust in informal information sources was associated with utilization of mammograms. CONCLUSIONS: Trust in one's own personal physician is associated with utilization of preventive health services. Blacks' relatively high distrust of their physicians likely contributes to health disparities by causing reduced utilization of preventive services. Health information disseminated to Blacks through informal means is likely to increase Blacks' utilization of preventive health services.