Delirium, a mental disorder that becomes established over a few hours or days, is characterised by fluctuating attention and cognitive states. This article reviews the disorder, which has all the features of an important geriatric syndrome: it appears mainly in persons older than 65 years of age, is closely linked with very prevalent diseases and complications arising in the elderly, and is the mode of presentation of many other diseases in this age group. We discuss diagnostic, clinical preventive and therapeutic aspects and analyse the most common risk and precipitating factors in our hospitalised patients from the viewpoint of clinical practice. Finally, we propose a scheme for the prevention and treatment of delirium.