The growing use of interoperable electronic health records is likely to have significant effects on the physician-patient relationship. This relationship involves two-way trust: of the physician in patients, and of the patients in their providers. Interoperable records opens up this relationship to further view, with consequences that may both enhance and undermine trust. On the one hand, physicians may learn (from additional records) that information from their patients is - or is not - to be trusted. On the other hand, patients may learn from the increased oversight made possible by electronic records that their trust in their physicians is - or is not - warranted. Release of information through new methods of surveillance may also undermine patient trust. The article concludes that because trust is fragile, attention to transparency and confidentiality in the use of interoperable electronic records is essential.