Despite the common occurrence of acute cognitive impairment in elderly emergency department (ED) patients, there is much uncertainty regarding the evaluation and management of this syndrome. We performed a retrospective cohort study of all patients 60 years of age and older transported by emergency medical services (EMS) to hospital EDs in Forsyth County, North Carolina, during 1990 specifically for evaluation of acute cognitive impairment. Five percent (227 of 4,688) of EMS transports during this time period were for the purpose of evaluation of acute cognitive impairment. Compared with community-dwelling patients (n = 105), nursing home patients (n = 47) had a higher prevalence of final ED diagnoses indicative of infection (42.5% v 13.3%) and a lower prevalence of diagnoses indicative of cerebrovascular disease (10.6% v 22.9%) as the etiology of cognitive impairment. The rates of hospitalization and mortality were 74.3% and 28.9%, respectively. The projected aging of the US population and the high prevalence of this syndrome among elderly patients make better understanding of this syndrome essential for ED providers.