Delirium is a common condition among hospital inpatients and people in long-term care settings. It is an acute confusional state associated with poor outcomes. Delirium is poorly recognised and managed despite evidence to suggest it is preventable in up to one third of cases. In July 2010, the National Institute for Health and Clinical Excellence published a comprehensive clinical practice guideline on the diagnosis, prevention and management of delirium. This article discusses the clinical features of delirium in relation to the guideline. It recommends that all clinical staff caring for older people should take on the responsibility to ‘think delirium’ and improve the quality of care for these patients.