OBJECTIVE: To investigate the risk factors for poststroke delirium and evaluate its influence on functional recovery after ischemic stroke. METHOD: Risk factors for delirium were investigated retrospectively in three hundred twenty nine acute ischemic stroke patients over 60 years of age. Among the 329 patients, sixty seven developed delirium. Data were analyzed between delirium group (n=22) and control group (n=22) according to age, sex, lesion location and clinical features. Korean modified Barthel index (K-MBI), Korean National Institutes of Health stroke scale (K-NIHSS) and Korean mini-mental state examination (KMMSE) were measured at second and sixth weeks after onset and compared for both groups. RESULTS: Parameters showing statistically significant difference between two groups were age over 80, hyponatremia, sleep deprivation, cognitive impairment and cardiogenic embolism. There was no significant difference in K-MBI, K-NIHSS and K-MMSE scores at second week between the two groups. The delirium group showed significantly less improvement in K-MBI and K-NIHSS scores compared to control group (9.5+/-10.2 vs 18.5+/-11.6, p=0.011; -0.7+/-1.2 vs -1.8+/-1.3, p=0.014). There was no significant improvement in K-MMSE score. CONCLUSION: The possible risk factors for delirium in acute ischemic stroke are age over 80, hyponatremia, sleep deprivation, cognitive impairment and cardiogenic embolism. Stroke patients with comorbid delirium showed poorer functional outcome. Delirium seems to have detrimental effect in functional recovery after stroke.