Social trust in health care organizations and interpersonal trust in physicians may be mutually supportive, but they also diverge in important ways. The success of medical care depends most importantly on patients' trust that their physicians are competent, take appropriate responsibility and control, and give their patients' welfare the highest priority. Utilization review and structural arrangements in managed care potentially challenge trust in physicians by restricting choice, contradicting medical decisions and control, and restricting open communication with patients. Gatekeeping and incentives to limit care also raise serious trust issues. We argue that managed care plans rather than physicians should be required to disclose financial arrangements, that limits be placed on incentives that put physicians at financial risk, and that professional norms and public policies should encourage clear separation of interests of physicians from health plan organization and finance.