Background: There are limited data on the performance of the pneumonia severity index (PSI) and CURB-65 (confusion, urea, respiratory rate, blood pressure, and age 65), which were originally developed for community-acquired pneumonia (CAP), for patients with healthcare-associated pneumonia (HCAP). Methods: The performances of PSI and CURB-65 were retrospectively evaluated in patients with HCAP compared to those with CAP using prospectively collected data between Jan 2008 and Dec 2010. Results: In total, 938 patients were eligible, consisting of 519 (55%) with CAP and 419 (45%) with HCAP. The PSI and CURB-65 had similar trends of increasing mortality with worsening risk class in both HCAP and CAP groups. In the HCAP group, however, the low-risk patients identified using CURB-65 had a higher 30-day mortality compared with the low-risk patients identified using PSI. Although the performances of PSI and CURB-65 in the HCAP group showed similar trends to those observed in the CAP group, the estimated areas under receiver operating characteristic curve of PSI (0.679, 95% CI 0.619-0.739) and CURB-65 (0.599, 95% CI 0.522-0.675) in the HCAP group were significantly lower than those in the CAP group (0.835, 95% CI 0.768-0.901 for PSI; 0.759, 95% CI 0.686-0.832 for CURB-65). Conclusions: The performances of PSI and CURB-65 for predicting 30-day mortality in patients with HCAP were comparable to those in patients with CAP. However, the discriminatory powers of PSI and CURB-65 for 30-day mortality were significantly 1lower in the HACP group than those in the CAP group.