"Acute confusion" is a syndrome, not just a symptom. Patients' cognition and behaviors change when they are confused. The elderly and children are common victims. Dementia and depression combined with acute confusion and make medical treatment more complicated. Literature uses delirium, acute mental status change, acute organic psychosis, reversible dementia, ICU psychosis, and postcardiotomy delirium as synonym of acute confusion. The contents of this article clearly present the nature, etiology, incidence, prevalence, onset, results and detect methods of acute confusion.