Acute confusional states are usually the result of a physical or mental illness and are usually temporary and reversible. Disorders that cause delirium are numerous and varied. They may include conditions that deprive the brain of oxygen or other substances. Delirium may be caused by diseases of body systems other than the brain, by poisons, by fluid/electrolyte or acid/base disturbances, and by other serious, acute conditions. Infections such as urinary tract infections or pneumonia may trigger delirium in individuals with preexistent damage to their brains (prior strokes, dementia).

The more preexistent brain disorders prior to an insult (infection, poisons, electrolyte derangement, lack of oxygen) the higher the likelihood of developing delirium.