Federal and state regulatory initiatives as well as court decisions increasingly require managed care organizations to disclose physician financial incentives and have raised the issue of disclosure by physicians themselves.These mandates are based on ethical and legal principles arising from the patient-physician relationship and the relationship between health plan sponsors and enrollees. Disclosing incentives also serves important policy objectives: it can inform enrollees' choice of plan, reinforce enrollees' capacity to understand and exercise other rights under managed care, and discourage use of compensation methods that might compromise patients' access to treatment. However, significant conceptual and practical questions remain about implementing a disclosure mandate. Unresolved issues include the timing, content, and scope of disclosure, the relationship of disclosure to patients' substantive rights, and the impact of disclosure on trust between patients and physicians. These uncertainties exemplify the challenges facing policymakers, plans, and physicians as they determine how best to inform patients about managed care.