Delirium is characterized by a sudden deterioration in cognitive function and an inability to sustain attention. It is a medical emergency that occurs in more than 20 percent of hospitalized elderly patients. Misdiagnosis is common and contributes to high morbidity and mortality. Patients may present in hypoactive, hyperactive or mixed states. Frail elderly patients are at greatest risk of delirium, especially those with dementia and multiple medical problems. Clinical history, physical examination and laboratory testing determine the most likely etiologies, such as medications (especially drugs with anticholinergic potential), infections and electrolyte disturbances. Effective management requires prompt treatment of the underlying pathology and maintenance of a supportive environment. It is often necessary to control agitation and prevent the complications of immobility in elderly patients with delirium. Although the long-term prognosis is guarded in elderly patients with delirium, sound geriatric care and a high index of suspicion can minimize the impact of delirium.