This study was conducted to propose an insight into the appropriateness of hospital length of stay(LOS) bydeveloping a severity-adjusted LOS model for patients with pneumonia, organism unspecified. The pneumoniarisk-adjustment model developed in this paper is based upon the 2006-2010 the Korean National HospitalDischarge in-depth Injury Survey. Decision tree analysis revealed that age, admission type, insurance type, and the presence of additionaldisorders(pleural effusion, respiratory failure, sepsis, congestive heart failure etc.) were major factors affecting theseverity-adjusted model using the Clinical Classifications Software(CCS). Also there was a difference in LOSamong the regional hospitals, especially the hospital LOS has not been efficiently managed inGyeongsangbuk-do, Jeollanam-do, Jeollabuk-do, Daejeon, and Busan. To appropriately manage hospital LOS, reliable statistical information about severity-adjusted LOS should begenerated on a national level to make sure that hospitals voluntarily reduce excessive LOS and manage maincauses of delayed discharge.