Delirium is a common neuropsychiatric syndrome in the elderly characterized by concurrent impairments in cognition and behaviors. The etiologies for delirium are often multifactorial and are due to underlying medical illnesses and/or due to medication effect. The diagnosis of delirium is often missed in elderly patients and this condition may be mislabeled as depression or dementia. Untreated, delirium can have devastating consequences in the elderly with high rates of morbidity and mortality. Available evidence indicates that early detection, reduction of risk factors, and better management of this condition can decrease its morbidity rates. In this review, we discuss the etiology, neurobiology, diagnosis, prevention, and treatments for this potentially lethal condition in the elderly.