The reported incidence of delirium in critically ill patients ranges widely - from 11% to 87%. Both in the recovery room as well as in the intensive care unit postoperative delirium is the most common psychiatric disease. Patients with ICU delirium have a significant higher 6-month mortality rate. Recent studies could show that the use of a validated delirium assessment tool significantly improves the ability of physicians and nurses to detect delirium in ICU patients. The following article gives a review about different assessment tools of ICU delirium and focuses on the differences between validated delirium scores.