Background: Health care-associated pneumonia (HCAP) has been proposed as a new category of respiratory infection. ATS/IDSA guidelines state that all patients with HCAP should receive empirical therapy directed at multidrug-resistant pathogens. However, recent data from other countries have reported a different picture of HCAP. Methods: We conducted a retrospective observational study of patients with HCAP and CAP who were hospitalized through the emergency department in January December 2008 at Samsung Medical Center, Seoul, Korea, and compared clinical characteristics, severity, distribution of pathogen, and outcomes. Results: In total, 345 patients hospitalized with pneumonia were eligible, 182 (52.8%) with HCAP and 163 (47.2%) with CAP. Patients with HCAP had greater comorbidity and higher Pneumonia Severity Index (PSI) score (P < 0.001). Although Streptococcus pneumoniae was the most frequently isolated pathogen in HCAP and CAP patients, the occurrence of potentially drug-resistant pathogens (29.3% vs. 13.0%; P = 0.044) and inappropriate initial antimicrobial treatment (24.6% vs. 8.7%; P = 0.032) were significantly higher in HCAP patients. Patients with HCAP had a longer duration of hospital stay (13 [8-18] vs. 8 [6-12] days; P < 0.001), and higher in-hospital mortality (19.2% vs. 7.4%; P = 0.001). In a multiple logistic regression analysis, however, in-hospital mortality was independently associated with higher PSI class (OR 2.82, 95% CI 1.19-6.70) and ICU admission (OR 15.37, 95% CI 3.58-66.05). Conclusions: Severity of illness, rather than type of pneumonia, was the main predicting factor for in-hospital mortality among patients with pneumonia hospitalized through the emergency department. (C) 2010 Elsevier Ltd. All rights reserved.