Delirium has been a recognised syndrome in the intensive care unit for some years. This systematic review reports risk factors for delirium studied in the intensive care unit. Four predisposing and 21 precipitating factors, including nine laboratory blood values and seven items relating to the use or the administration of medication, were found to influence the onset of delirium in the intensive care unit in six publications. The APACHE II score and hypertension were the only factors reported twice. Risk factors for the development of intensive care delirium were understudied and underreported in the literature.