AbstractObjective:To determine change in rates of postoperative pneumonia and ventilator-associated pneumonia among patients hospitalized in the United States during 2009–2019.Design:Retrospective cohort study.Patients:Patients hospitalized for major surgical procedures, acute myocardial infarction, heart failure, and pneumonia.Methods:We conducted a retrospective review of data from the Medicare Patient Safety Monitoring System, a chart-abstraction–derived database including 21 adverse-event measures among patients hospitalized in the United States. Changes in observed and risk-adjusted rates of postoperative pneumonia and ventilator-associated pneumonia were derived.Results:Among 58,618 patients undergoing major surgical procedures between 2009 and 2019, the observed rate of postoperative pneumonia from 2009–2011 was 1.9% and decreased to 1.3% during 2017–2019. The adjusted annual risk each year, compared to the prior year, was 0.94 (95% CI, 0.92–0.96). Among 4,007 patients hospitalized for any of these 4 conditions at risk for ventilator-associated pneumonia during 2009–2019, we did not detect a significant change in observed or adjusted rates. Observed rates clustered around 10%, and adjusted annual risk compared to the prior year was 0.99 (95% CI, 0.95–1.02).Conclusions:During 2009–2019, the rate of postoperative pneumonia decreased statistically and clinically significantly in among patients hospitalized for major surgical procedures in the United States, but rates of ventilator-associated pneumonia among patients hospitalized for major surgical procedures, acute myocardial infarction, heart failure, and pneumonia did not change.