Introduction: Delirium is a very prevalent cognitive impairment in elderly inpatients, but it often goes undetected, especially in the emergency department (ED). The tools currently available to screen or diagnose patients at risk of delirium are very time-consuming and are impossible to systematically perform in the ED environment. For this reason, short tests are necessary to screen for delirium in this fast-paced setting. The objective of this study was to evaluate the performance of the French version of the Rapid Assessment Test for Delirium (4AT) for the detection of delirium and cognitive impairment in older patients. The 4AT takes less than 2 minutes to administer, which is a great advantage on the others tests. Methods: The study was conducted in four emergency departments across the province of Québec. Participants were independent or semi-independent patients aged 65 and older, admitted to hospital and who had an 8-hour exposure to the ED. The Telephone Interview for Cognitive Status (TICS) was administered at the initial interview and the Confusion Assessment Method (CAM) as well as the 4AT were administered to patients twice a day during their ED or hospital stay. The 4AT’s sensitivity and specificity were compared to that of the CAM (for delirium), and to that of the TICS (for cognitive impairment). Results: 324 patients were included in the study, with a mean age of 76 years old. Among the recruited participants, 21 (6.5%) had a prevalent delirium according to the CAM, and 30 (10.2%) had an incident delirium. According to the 4AT, 48 patients (14.9%) had cognitive impairment and 81 (25.2%) had a prevalent delirium. According to the TICS, 87 patients (29.2%) have cognitive impairment. The 4AT has a sensitivity of 68,4% (IC 95% : 47,5-89,3) and a specificity of 73.2% (IC 95% : 67,8-78,7) for delirium, and a sensitivity of 50% (IC 95% : 35,9-64,1) and a specificity of 87,0% (IC 95% : 81,2-92) for cognitive impairment. Conclusion: The French Version of the 4AT could be a fast and reliable screening tool for delirium and cognitive impairment in ED. Further research is necessary for its validation in the ED.