The objective of this study was to compare the results of the Confusion Assessment Method (CAM) obtained by a trained non-physician interviewer to those obtained by a geriatrician, among a sample of elderly patients seen in an emergency room. A group of 110 elderly patients (> or =66 years) were evaluated in the emergency room by a lay interviewer. The geriatrician conducted an interview in the presence of the lay interviewer. Subsequently, the geriatrician and the lay interviewer completed a CAM checklist independently. Kappa statistics, sensitivity, specificity, positivity predictive value (PPV), and negative predictive value (NPV) for the geriatrician's and lay interviewer's results with the CAM diagnostic algorithm were compared. The kappa coefficient was 0.91, the sensitivity 0.86, the specificity 1.00, the PPV 1.00, and the NPV 0.97. In conclusion, the CAM used by a trained lay interviewer in the emergency room is sensitive, specific, reliable and easy to use for the identification of patients with delirium. The under-recognition and under-treatment of delirium is a major health issue and has important clinical and financial implications. The implementation of systematic screening in populations at risk could increase the rate of early detection and lead to the appropriate management of delirious patients.