While there is little question that advancing chronological age is intimately implicated in the brain's enhanced vulnerability to acute confusional states, the nature and dynamics of this relationship, until recently, have managed to escape sustained empirical scrutiny. Despite the fact that the syndrome has been described in the medical literature for over 2,000 years, despite the presence of many anecdotal reports on delirium in the clinical literature, and despite its long-rooted association with high rates of morbidity and mortality in senescence, surprisingly little hard data has been collected regarding distribution of the syndrome in the general population, critical aspects of differential diagnosis, the spectrum of syndromal phenomenology, or the nature of clinical course and outcome. Additionally, many questions regarding etiology, pathophysiology, and pathology have received less than adequate research attention.