In a study of 17,290 hospitalized adults with community-acquired pneumonia (CAP), 12.0% were found to have inappropriate diagnosis, defined as receiving CAP-directed antibiotic therapy with fewer than two signs/symptoms of pneumonia or no radiographic findings. Older adults, those with dementia, and those with altered mental status were at higher risk. Of those inappropriately diagnosed, 87.6% received full antibiotic courses, which were associated with higher rates of antibiotic-associated adverse events. The study highlights the prevalence of inappropriate CAP diagnosis, particularly among vulnerable populations, and suggests that full-course antibiotic treatment may be harmful. The findings emphasize the need for improved diagnostic accuracy and appropriate antibiotic use to reduce harm from unnecessary treatment. The study used a validated metric endorsed by the National Quality Forum to define inappropriate diagnosis and analyzed outcomes including mortality, readmission, and adverse events. The results indicate that inappropriate diagnosis is common and that full antibiotic courses may increase the risk of adverse events. The study underscores the importance of balancing the risks of underdiagnosis and overdiagnosis in hospitalized patients with CAP.In a study of 17,290 hospitalized adults with community-acquired pneumonia (CAP), 12.0% were found to have inappropriate diagnosis, defined as receiving CAP-directed antibiotic therapy with fewer than two signs/symptoms of pneumonia or no radiographic findings. Older adults, those with dementia, and those with altered mental status were at higher risk. Of those inappropriately diagnosed, 87.6% received full antibiotic courses, which were associated with higher rates of antibiotic-associated adverse events. The study highlights the prevalence of inappropriate CAP diagnosis, particularly among vulnerable populations, and suggests that full-course antibiotic treatment may be harmful. The findings emphasize the need for improved diagnostic accuracy and appropriate antibiotic use to reduce harm from unnecessary treatment. The study used a validated metric endorsed by the National Quality Forum to define inappropriate diagnosis and analyzed outcomes including mortality, readmission, and adverse events. The results indicate that inappropriate diagnosis is common and that full antibiotic courses may increase the risk of adverse events. The study underscores the importance of balancing the risks of underdiagnosis and overdiagnosis in hospitalized patients with CAP.