Missed and delayed diagnoses are an increasingly recognized patient safety problem. A common undiagnosed symptom in outpatient medicine is chest pain. This retrospective cohort study compared outcomes for three groups of patients with chest pain: those whose pain remained undiagnosed after 6 months versus those diagnosed with either coronary artery disease or a verified noncardiac cause of chest pain. Only a minority of the undiagnosed patients underwent diagnostic testing for coronary artery disease. The highest risk of myocardial infarction was in patients with diagnosed coronary artery disease, but undiagnosed patients were more likely to have a myocardial infarction than those with verified noncardiac disease. The authors conclude that patients without a timely diagnosis merit further evaluation to reduce the risk of cardiovascular events.