This patient experienced the following serious medical error: failure to recognize that the atrial fibrillation was not new. Had the covering cardiologist discovered the history of atrial fibrillation, routine anticoagulation before cardioversion would have been recommended, and this would have likely prevented the subsequent fatal embolic stroke. Many arguments could be made to support the decision of the hospital not to disclose the error to the widower. Chief among them might be concern for his psychological well-being, underlying dementia, lack of surrogates, and the clinical uncertainty surrounding the fatal event (ie, the possibility that the embolic stroke might have been an independent event unrelated to cardioversion). In such situations, the reasons not to disclose can look very appealing. Cases in which an error is not apparent or in which health-care workers believe that patients or families might not understand the disclosure pose special problems for physicians, and data16 suggest that disclosure is less likely to happen in these instances. Other reasons may operate more subconsciously, for example, the desire to avoid a lawsuit, even if seemingly unlikely in this case, and the embarrassment of the error compounded by the irony of the widower's letter thanking the medical center for its excellent care.