Delirium is defined as a disturbance of consciousness with cognitive changes or perceptual disturbances, which has developed over a short period of time, and is caused by a medical condition or a postsurgical state. Although historically dismissed as an inconvenient and transient problem, recent studies have reported that delirium is associated with more complications, increased length of hospital stay, and higher mortality. Although delirium is a prevalent condition after cardiothoracic surgery and in the intensive care unit (ICU), the condition appears to be largely underdiagnosed. Several detection tools have been developed for routine monitoring of delirium by nonpsychiatric personnel in the ICU, such as the Confusion Assessment Method for the Intensive Care Unit and the Intensive Care Delirium Screening Checklist. Management includes treatment of underlying disorders, nonpharmacological measures and symptomatic drug therapy. There is a need for well-designed randomized, double-blind, placebo-controlled trials on drug treatment.