<p>Vital signs are essential for monitoring and prognostication in the emergency department (ED); however, they may not fully capture the complexity of frailty in older adults. In this multicenter retrospective study of 932 older patients who visited the EDs of three tertiary university hospitals between August 1 and October 31, 2023, we investigated the prognostic value of the Clinical Frailty Scale (CFS) in older patients in the ED and its potential to improve existing vital sign-based scoring systems. The primary outcomes were hospital admission, intensive care unit (ICU) admission, and in-hospital mortality. The AUROC was used to evaluate and compare the predictive performance of CFS, qSOFA, NEWS2, and REMS scores individually and in combination. Combining the CFS with these scores significantly improved predictive accuracy compared to individual scores alone. For hospital admission, the AUROCs were 0.715 (95% CI 0.685–0.744), 0.723 (95% CI 0.693–0.752), and 0.688 (95% CI 0.657–0.718) for CFS + qSOFA, CFS + NEWS2, and CFS + REMS, respectively. For ICU admission, the AUROCs were 0.730 (95% CI 0.701–0.759), 0.714 (95% CI 0.684–0.743), and 0.707 (95% CI 0.677–0.736), respectively. For in-hospital mortality, the AUROCs were 0.798 (95% CI: 0.771–0.823), 0.774 (95% CI: 0.746–0.801), and 0.819 (95% CI: 0.793–0.843), respectively, indicating excellent performance. Incorporating frailty assessment using the CFS enhances risk stratification in older patients in the ED by complementing vital sign-based scores. This provides a more comprehensive assessment, enabling better informed clinical decisions. This study supports employing routine frailty assessment in the ED and the development of enhanced risk stratification tools that incorporate frailty.</p>