Traditionally, pneumonia developing in patients outside the hospital is categorized as community acquired, even if these patients have been receiving health care in an outpatient facility. Accumulating evidence suggests that health-care-associated infections are distinct from those that are truly community acquired. To characterize the microbiology and outcomes among patients with culture-positive community-acquired pneumonia (CAP), health-care-associated pneumonia (HCAP), hospital-acquired pneumonia (HAP), and ventilator-associated pneumonia (VAP). A retrospective cohort study based on a large US inpatient database. A total of 4,543 patients with culture-positive pneumonia admitted into 59 US hospitals between January 1, 2002, and December 31, 2003, and recorded in a large, multi-institutional database of US acute-care hospitals (Cardinal Health-Atlas Research Database; Cardinal Health Clinical Knowledge Services; Marlborough, MA). Culture data (respiratory and blood), in-hospital mortality, length of hospital stay (LOS), and billed hospital charges. Approximately one half of hospitalized patients with pneumonia had CAP, and > 20% had HCAP. Staphylococcus aureus was a major pathogen in all pneumonia types, with its occurrence markedly higher in the non-CAP groups than in the CAP group. Mortality rates associated with HCAP (19.8%) and HAP (18.8%) were comparable (p > 0.05), and both were significantly higher than that for CAP (10%, all p < 0.0001) and lower than that for VAP (29.3%, all p < 0.0001). Mean LOS varied significantly with pneumonia category (in order of ascending values: CAP, HCAP, HAP, and VAP; all p < 0.0001). Similarly, mean hospital charge varied significantly with pneumonia category (in order of ascending value: CAP, HCAP, HAP, and VAP; all p < 0.0001). The present analysis justified HCAP as a new category of pneumonia. S aureus was a major pathogen of all pneumonias with higher rates in non-CAP pneumonias. Compared with CAP, non-CAP was associated with more severe disease, higher mortality rate, greater LOS, and increased cost.