In this systematic review, the authors pooled over 80,000 patients and 760 harmful diagnostic errors from 22 studies and estimated the prevalence of harmful diagnostic errors among hospitalized patients to be 0.7% (95% CI, 0.5-1.1%). Fourteen common diagnoses account for more than half of all missed or delayed diagnoses, with the most frequent being cancer (11%) and pulmonary embolism (9.6%). Extrapolated to the United States, these estimates correspond to approximately 249,900 harmful diagnostic errors each year.