Delirium is a common development in at-risk older patients hospitalized for acute illness or postoperative care. Although delirium's risk factors are well documented, less is known about its pathophysiology and long-term prognosis or about the relationship between delirium, dementia, and depression. Evaluation and management of delirium is a medical emergency. Diagnostic tools include the Confusion Assessment Method rating scale, patient history from capable informants, and physical/mental examinations. Management consists of prevention, treatment of underlying causes or associated factors, supportive care, and pharmacologic intervention (as indicated). Studies that have looked at the reversibility of delirium suggest that patients often are slow to recover their previous level of function.