Late life psychosis may be caused by organic conditions including: delirium, dementia, drug intoxication or withdrawal, or a general medical condition. In these situations there should be evidence of a temporal relationship between the psychosis and the underlying condition. Around 60% of older adults presenting with new onset psychosis have an identifiable underlying organic cause. If an underlying medical condition can be excluded, and there is no evidence to support a diagnosis of delirium or dementia, then the cause of psychosis may be functional. This is more likely if there is a family or personal history of mental illness.