Misdiagnosis of acute aortic syndrome (AAS), which includes aortic dissection, can result in serious patient harm or death. Based on a retrospective cohort including 1,299 cases of AAS in Ontario, Canada, between 2003-2018, researchers estimated that the rate of AAS misdiagnosis was 12.5%. Presentation to a non-teaching hospital or non-cardiac emergency department increased the odds of misdiagnosis. Mortality and surgical intervention were similar in missed and non-missed cases of AAS.