Delirium syndrome is a group of syndromes characterized by widespread cognitive impairment, especially impaired consciousness. It is often caused by diffuse, temporary poisoning infection or metabolic disorder in the brain. Because it often occurs in poisoning infection, brain trauma and other diseases with acute onset, short course and rapid development of lesions, it is also called acute brain syndrome or acute confusional state. Delirium syndrome is the most common mental disorder in general hospitals, accounting for about 5% to 15% of internal and surgical patients, and most of them can recover. The following six types of patients are more likely to develop delirium: ① the elderly, ② children, ③ after heart surgery, ④ burns, ⑤ brain damage, and ⑥ drug dependence. Recently, two general hospitals abroad conducted an epidemiological study and found that 30% and 50% of the elderly aged 70 and over showed signs of delirium, respectively. However, because most elderly patients with physical diseases often stay at home for treatment when they have mild mental confusion, the incidence of delirium in the elderly appears to be much higher than generally estimated.