Delirium is a mental disorder of acute onset and fluctuating course, characterized by disturbances in consciousness, orientation, memory, thought, perception, and behavior. It occurs in up to 50% of elderly hospital inpatients, many with preexisting dementia, and is associated with significant increases in functional disability, length of hospital stay, rates of death, and health care costs. Despite its clinical importance, delirium often remains undetected or misdiagnosed as dementia or other psychiatric illness. Awareness of the etiologies and risk factors of delirium should enable nurses to focus on patients at risk and to recognize delirium symptoms early. Knowledge of pharmacological and nonpharmacological treatments for delirium will provide the nurse with an arsenal of potential interventions in the care of the delirious hospitalized elder.