A psycho-organic disorder such as delirium is a frequently occurring and serious disorder especially on Intensive Care units. Nowadays, more attention is paid to this problem by physicians, nurses and by researchers, but assessment of delirium in all ICU patients is still not common practice. If patients are not screened for delirium in a standard manner, once or several times a day, the delirium diagnose will be missed. In this systematic review we describe and analyse six delirium screening instruments available from the literature: the Cognitive Test for Delirium (CTD), the abbreviated CTD, Intensive Care Delirium Screening Checklist (ICDSC), Delirium Detection Score (DDS), NEECHAM confusion scale and the Confusion Assessment Method-ICU (CAM-ICU). Each assessment tool its characteristics, reliability and validity testing is briefly described. We conclude that important delirium criteria are not integrated into some screening tools (CTD and aCTD, DDS), or an important group of ICU patients cannot be tested (NEECHAM). The ICDSC and the CAM-ICU appear to represent the most feasible instruments for delirium screening in the ICU. Of these two tests, the CAM-ICU prevails because of the validated Dutch version and its reported high sensitivity and specificity. Copyright © 2010, Nederlandse Vereniging voor Intensive Care. All Rights Reserved.