The epidemiology of pneumonia has likely evolved in recent years, reflecting an aging population, changes in population immunity, and socioeconomic disparities. Using the National (Nationwide) Inpatient Sample, estimated numbers and rates of pneumonia-associated hospitalizations for 2001-2014 were calculated. A pneumonia-associated hospitalization was defined as one in which the discharge record listed a principal diagnosis of pneumonia or a secondary diagnosis of pneumonia if the principal diagnosis was respiratory failure or sepsis. There were an estimated 20,361,181 (SE, 95,601) pneumonia-associated hospitalizations in the United States during 2001-2014 (average annual age-adjusted pneumonia-associated hospitalization rate of 464.8 per 100,000 population [95% CI, 462.5-467.1]). The average annual age-adjusted pneumonia-associated hospitalization rate decreased over the study period (P < .0001). In-hospital death occurred in 7.4% (SE, 0.03) of pneumonia-associated hospitalizations. Non-Hispanic American Indian/Alaskan Natives and non-Hispanic blacks had the highest average annual age-adjusted rates of pneumonia-associated hospitalization of all race/ethnicities at 439.2 (95% CI, 415.9-462.5) and 438.6 (95% CI, 432.5-444.7) per 100,000 population, respectively. During 2001-2014, the proportion of pneumonia-associated hospitalizations colisting an immunocompromising condition increased from 18.7% (SE, 0.2) in 2001 to 29.9% (SE, 0.2) in 2014. Total charges for pneumonia-associated hospitalizations in 2014 were over $84 billion. Pneumonia is a major cause of morbidity and mortality in the United States. Differences in rates and outcomes of pneumonia-associated hospitalizations between sociodemographic groups warrant further investigation. The immunocompromised population has emerged as a group experiencing a disproportionate burden of pneumonia-associated hospitalizations. Copyright © 2017 American College of Chest Physicians. All rights reserved.