Delirium is a serious and common syndrome characterized by acute deterioration of mental status. Patients show attentional deficits and commonly also altered levels of arousal and psychotic features. Detection can be assisted through use of validated tools such as the 4AT. Delirium is associated with multiple adverse outcomes including patient and carer distress, increased length of hospital stay, risk of future dementia, new institutionalization and death. Old age, dementia and frailty are the main predisposing factors, but there are a number of modifiable risk factors that are important within hospital environments.