Misdiagnosis may delay appropriate treatment and/or result in improper treatment. In this study of more than 17,000 patients with a discharge diagnosis of community-acquired pneumonia (CAP), 12% did not meet the diagnostic criteria. 25% of inappropriately diagnosed patients experienced an antibiotic-associated adverse event. Older adults, those with dementia, and those presenting with altered mental status were more likely to be inappropriately diagnosed.