The purpose of this paper was to contribute to a new conceptual understanding of delirium by reviewing evidence related to its prevention, treatment, and outcome. The review process involved a systematic search of the literature on each topic, assessment of the validity of the studies retrieved, and examination of their results. The literature search identified 10 studies on prevention, 13 studies on treatment, and 15 studies on outcome. Most studies had methodological limitations. Abroad spectrum of interventions appeared to be modestly effective in preventing delirium in young and old surgical patients but not elderly medical patients; systematic detection and intervention programs and special nursing care appeared to add large benefits to traditional medical care in young and old surgical patients and modest benefits in elderly medical patients; haloperidol, chlorpromazine, and mianserin appeared to be useful in controlling the symptoms of delirium in both surgical and medical patients; and good levels of premorbid function seemed to be related to better outcomes. Although the above findings do not contribute to a new conceptual understanding of delirium, they do suggest directions for further research on the treatment of delirium.