Delirium (acute confusional state) is a common condition in older people, affecting up to 30% of all older patients admitted to hospital. Patients who develop delirium have high mortality, institutionalisation and complication rates, and have longer lengths of stay than non-delirious patients. Delirium is often not recognised by clinicians, and is often poorly managed. Delirium may be prevented in up to a third of older patients. The aim of this guideline update is to aid prevention as well as the recognition of delirium and to provide guidance on how to manage these complex and disadvantaged patients.