An increasing number of elderly patients are presenting to the emergency department. Numerous studies have observed that emergency physicians often fail to identify and diagnose delirium in the elderly. These studies also suggest that even when emergency physicians recognized delirium, they still may not have fully appreciated the import of the diagnosis. Delirium is not a normal manifestation of aging and, often, is the only sign of a serious underlying medical condition. This article will review the significance, definition, and principal features of delirium so that emergency physicians may better appreciate, recognize, evaluate, and manage delirium in the elderly.