Improving diagnosis in health care is a moral, professional and public health imperative, according to the U.S. National Academy of Medicine. However, little is known about the full scope of harms related to medical misdiagnosis — current estimates range widely. Using novel methods, a team from the Johns Hopkins Armstrong Institute Center for Diagnostic Excellence and partners from the Risk Management Foundation of the Harvard Medical Institutions sought to derive what is believed to be the first rigorous national estimate of permanent disability and death from diagnostic error.