Objectives : Schizophrenia and other psychiatric disorder are associated with an increased risk of premature death. For decades, there have been reports of shorter life expectancy among those with severe mental illness. The purpose of this study was to compare the risk of mortality among institutionalized population, treated for severe mental illness to control group who did not have severe mental illness. Methods : The medical records and the death certificates of 2,029 institutionalized population who had died from 1985 to 2003 in Kkottongnae were investigated. Results : The mean age of the death of severe mental illness(SMI) group(51.4${pm}$15.3 years old) was lower than that of non-severe mental illness(non-SMI) group(65.0${pm}$19.3 years old) and it was statistically significant(p<0.0001). The most causes of death among the SMI group were respiratory diseases(23.3%), infectious disease (13.0%) and digestive disease(12.3%). Also, we found that the death due to injuries of the SMI group(8.9%) were three times higher than that of non-SMI group(2.5%). The most causes of death among the non-SMI group were respiratory disease(26.3%), circulatory disease(26.2%) and neoplasm(10.8%). Conclusion : The SMI group demonstrated higher mortality rates compared with the rate in the non-SMI group. The finding suggests that careful intervention is needed not only for menal health but also physical health in long-term facilities.