Delirium or acute confusional state is a condition that lies within the boundaries of psychiatry and other medical specialties. It is defined as a syndrome characterized by a fluctuating cognitive impairment of acute onset. The pathogenesis is multifactorial and it frequently appears in elderly patients admitted to general hospitals. Delirium carries a high mortality and it prolongs hospital stay. Its diagnosis if often overlooked and the treatment is inadequate or belated. This article discusses the most efficient procedures to diagnose and treat delirium. The review was based on a systematic search in the literature using the key words delirium, acute mental syndrome, acute confusional state and organic mental syndrome. Articles were selected according to their relevance and methodological accuracy