Although diagnostic errors represent an important cause of preventable patient harm as well as a common and expensive source of malpractice litigation, they have received little attention until recently. Misdiagnosis or delayed diagnosis of common conditions, such as acute myocardial infarction (AMI), occurs frequently. In this study, researchers sought to assess whether a correct initial diagnosis had an impact on the mortality of patients with AMI. They looked at a cohort of patients over 9 years across 243 acute care hospitals in England and Wales with discharge diagnoses of ST-elevation myocardial infarction and non–ST-elevation myocardial infarction. The authors concluded that almost a third of patients were initially misdiagnosed and that this was associated with increased mortality. A PSNet Annual Perspective discussed recent advances in thinking about diagnostic error.