Most patients in the United States depend on physicians who have financial relationships with the healthcare industry. These physician-industry relationships represent a conflict of interest: a potential clash between the physicians’ professional responsibilities and their self-interest. We conducted a randomized field experiment to assess the impact of written disclosures of physicians’ conflict of interest on patients’ appointment attendance, knowledge of these conflicts of interest, and their trust in their physician and hospital. Patients (N = 1903) attending outpatient clinics at a large U.S. academic hospital from 2015 to 2016 who had appointments with physicians earning more than $20,000 from industry in the last year were randomized to receive (or not receive) disclosures of their physicians’ financial conflicts of interest (with or without explanation of the risks and/or benefits of such conflicts) in their appointment-reminder letters. There were no differences across condition in missed or cancelled appointments. For patients who attended eligible appointments with their physician and completed the post-appointment survey (N = 867/1276; 68% response rate), the disclosure intervention revealed significant improvement in patients’ knowledge of their physicians’ financial relationships but no significant differences in patients’ trust in their physician or hospital. Risk and benefit framings of financial relationships did not significantly affect any outcomes. These findings highlight that although mailed financial conflict of interest disclosures are effective as an educational tool, disclosure cannot be a panacea to addressing physician-industry relationships if the intended purpose is for patients to assimilate the information into their decision-making and account for potential physician bias.