Objectives:It is known that delirium is common among elder patients and is associated poor clinical outcomes. As elderly patients are increasing in emergency department(ED), the prevalence of delirium should be on the rise. However delirium has been under-recognized by medical team. Our study was designated to evaluate the frequency, the clinical effect and risk factors of delirium of hospitalized elder patients in ED. Methods:We retrospectively reviewed elderly patients admitted to general ward after over 24 hours hospitalization in ED between January 2008 and December 2008. examined the frequency and assessed the clinical effect and risk factors. Results:Among 414 patients, 42 patients(10.1%) developed delirium in ED over 12 month period studied. The development of delirium in ED was associated with significant poor outcomes ; increased hospital mortality and prolonged hospital stays. Independent risk factors of delirium were stroke, metabolic derangements, dementia, hemodynamic instability, depression. Conclusion:ED environment can be important risk factors of delirium, thus ED physician should try to recognize and correct the possible risk factors of delirium earlier and in particular, should try to reduce exposure time to the ED environment in elderly patients.