Opinions are deeply divided over whether rewarding physicians for lowering costs decreases trust in physicians or insurers. To explore the effects of disclosing physician payment methods in HMOs, members of two similar HMO plans were randomized to intervention and control groups, and the experimental arm was told how the HMO paid their primary care physician. Separate disclosures were developed for each plan, one describing primarily capitation payment, and the other (mixed-incentive plan) describing fee-for-service payment with a bonus that rewards cost savings, satisfaction, and preventive services. The disclosures pointed out more of the positive than the negative features of these incentives. We found that the disclosures doubled the number of subjects with substantial knowledge of the physician incentives and halved the number with no knowledge. Nevertheless, the disclosures had no negative effects on trust of either physicians or insurers. The capitated plan disclosure had a small positive effect on trust of physicians. Disclosing the positive and negative features of incentives and increasing knowledge of these incentives does not, in the short term, reduce trust in physicians or insurers and may have a mild positive impact on physician trust, perhaps as a consequence of displaying candor and increasing understanding of positive features.