Introduction Up to half of head and neck cancer (HNC) patients undergoing major surgery are frail, resulting in increased postoperative morbidity and mortality1. Despite guidelines recommending routine frailty screening, no validated gold standard tool exists for patients undergoing major HNC surgery. Methods This prospective study evaluated the prognostic accuracy of four frailty tools: Clinical Frailty Scale (CFS), Geriatric 8 (G8), and the 5 and 11 item Modified Frailty Index (mFI) in predicting postoperative Clavien-Dindo complications in 50 patients aged 70 and older undergoing HNC surgery. Results The CFS demonstrated the highest predictive capacity for severe complications, with frailty (CFS ≥ 5) increasing odds five-fold (OR = 5.16, 95% CI: 1.12–23.69, p = 0.035; AUC = 0.70). Age ≥ 86 years was also predictive, with each additional year increasing complication odds by 15% (OR = 1.15, 95% CI: 1.02–1.30, p = 0.018; AUC = 0.71). The G8, mFI-5, and mFI-11 had limited predictive utility (AUC = 0.30, 0.50, and 0.58, respectively). Conclusion CFS defined frailty provides the greatest prognostic accuracy compared to other tools, and is a more accurate than chronological age in patients under 86 years. Age alone stratified risk in patients ≥ 86 years. Integrating CFS into preoperative workflows could improve surgical decision-making and guide perioperative interventions to improve patient outcomes. References 1.Cleere EF, Davey MG, O'Neill JP. "Age is just a number"; frailty as a marker of peri-operative risk in head and neck surgery: Systematic review and meta-analysis. Head and Neck-Journal for the Sciences and Specialties of the Head and Neck 2022; 44(8):1927-1939.