Postoperative delirium is a common syndrome that is often mistaken for other psychiatric conditions, particularly depression. Numerous investigators have found a clear convincing association between delirium and increased morbidity and mortality. For this reason, greater attention should be focused on accurate clinical diagnosis. In this article, pre- and postoperative risk factors are reviewed. Lastly, areas demanding immediate further investigation are identified. In particular, outcome studies with particular emphasis on the role of age and prior drug exposure are urgently needed.