Patients with delirium, dementia, depression, and schizophrenia were administered a newly developed test designed to identify delirium in an intensive care unit (ICU) setting. Two alternate forms of the Cognitive Test for Delirium (CTD) were highly correlated. The delirium patients performed least well, and an optimal cutoff score derived from relative-operating characteristic analysis resulted in a sensitivity of 100% and a specificity of 95%. In a follow-up study, the Mini-Mental State Exam could not be administered to 42% of the ICU patients who completed the CTD. Early identification of delirium with the CTD may lead to timely treatment of specific etiologic conditions and a reduction in mortality and morbidity.