Abstract Purpose We aimed to study the use of The 4 ‘A’s test (4AT), a rapid delirium screening tool, performed upon Emergency Department (ED) admission, and to characterize older patients admitted to the ED with and without sepsis in terms of delirium features. Methods In this prospective cohort study, we included patients aged ≥ 65 years, admitted to the ED with suspected sepsis. ED nurses and doctors performed delirium screening with 4AT within two hours after ED admission, and registered the time spent on the screening in each case. Sepsis and delirium during the hospital stay were diagnosed retrospectively, according to recommended diagnosis criteria. Results Out of the 196 patients included (mean age 81 years, 60% men), 100 patients fulfilled the sepsis diagnosis criteria. The mean 4AT screening time was 2.5 Minutes. In total, 114 patients (58%) had a 4AT score ≥ 1, indicating cognitive impairment, upon ED admission. Sepsis patients more often had a 4AT score ≥ 4, indicating delirium, than patients without sepsis (40% vs. 26%, p < 0.05). Out of the 100 patients with sepsis, 68 (68%) had delirium during the hospital stay, as compared to 34 out of 96 patients (35%) without sepsis (p < 0.05). Conclusion Delirium screening upon ED admission, using 4AT, was feasible among patients aged ≥ 65 years admitted with suspected sepsis. Two out of three patients had at least one feature of delirium upon admission. The prevalence of delirium during the hospital stay was high, particularly in patients with sepsis. Graphic abstract