Background: Delirium is a common neuropsychiatric syndrome characterized by disturbance of attention and consciousness developing over a short period of time. Symptoms tend to fluctuate during the course of the day. Delirium is by definition a direct physiological consequence of a general medical condition and is probably the most common presenting symptom of disease in old age., Material and Methods: Literature review based on search on PubMed and Medline up to 31 December 2001 and a summary of several doctoral theses and our own clinical experience., Results and Interpretation: Several recent intervention studies have clearly shown that delirium can be prevented and treated. Successful intervention programmes have been multifactorial and interdisciplinary, including assessment and treatment of underlying causes as well as prevention and treatment of factors endangering cerebral metabolism. In particular, cerebral hypoxemia caused by i.e. sleep-apnoea syndrome, anaemia, hypotension, pulmonary diseases, and heart failure is often easily prevented and treated. Excellent nursing care seems to be a prerequisite for successful prevention and treatment of delirium. Acceptable scientific evidence for pharmacological treatment is still lacking; it is sometimes necessary but should be used with caution. If sedation is acceptable, clomethiazole is the drug of choice but if the delirium is complicated by frightening hallucinations and agitation, haloperidol or risperidone can be used but only for short periods. Cholinesterase inhibitors are probably a better choice, though randomised treatment studies are still lacking.