Although missed and delayed diagnoses are known to contribute to morbidity and mortality, measuring the extent of their impact on patient safety remains a challenge. In this study, researchers sought to identify missed diagnosis of acute myocardial infarction (AMI) using administrative data, an approach similar to prior studies of diagnostic accuracy. They suggest that patients treated in the emergency department for chest pain or a cardiac condition and released, who were then hospitalized for AMI within 7 days of that visit experienced a missed AMI diagnosis. The authors estimate that nearly 1% of AMI admissions represent a prior missed diagnosis. Younger patients and black patients had higher odds of missed diagnosis, raising concerns for disparities in the diagnostic process. Conversely, teaching hospital status and availability of cardiac catheterization were associated with lower odds of missed diagnosis, suggesting that settings where AMI is more commonly treated have higher diagnostic accuracy, mirroring earlier research on cognition and diagnosis. This study represents a promising approach for identifying missed diagnosis for other common conditions using available data.