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Objectives: Prognostic tools with evidence for external validity in routine clinical practice are needed to align care with patients' preferences and deliver timely supportive services. Current models have limited, if any, evidence for external validity and none have been implemented and evaluated in clinical practice on a large scale. This study sought to provide evidence for external validity in a real life setting of the Cohen prognostic model that integrates actuarial factors with the 'Surprise Question' to assess 6-month, 12-month and 18-month survival of prevalent haemodialysis patients., Methods: Cross-sectional study of 1372 patients in a Canadian university-based programme between 2010 and 2019. Survival probabilities were compared with observed survival. Discrimination and calibration were assessed through predicted risk-stratified observed survival, cumulative AUC, Somer's Dxy and a calibration slope estimate., Results: Discrimination performance was moderate with a C statistic of 0.71-0.72 for all three time points. The model overpredicted mortality risk with the best predictive accuracy for 6- month survival. The differences between observed and mean predicted survival at 6 months, 12 months and 18 months were 3.2%, 8.8% and 12.9%, respectively. Kaplan-Meier curves stratified by Cox-based risk group showed good discrimination between high-risk and low-risk patients with HR estimates (95% CI): C2 vs C1 3.07 (1.57-5.99), C3 vs C1 5.85 (3.06-11.17), C4 vs C1 13.24 (6.91-25.34))., Conclusions: The Cohen prognostic model can be incorporated easily into routine dialysis care to identify patients at high risk for death over 6 months, 12 months and 18 months and help target vulnerable patients for timely supportive care interventions., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)