Background <p>As the population ages, factors affecting prognosis after dialysis initiation in very elderly patients remain unclear. We aimed to develop a prognostic score to predict short-term survival in this group.</p> Methods <p>This retrospective cohort study included 116 patients aged 85 or older who initiated hemodialysis at our hospital between 2010 and 2023, out of a total of 2279 patients. Using a Cox regression model, we analyzed factors affecting 3-year all-cause mortality. Based on these analyses, a prognostic scoring system was developed to predict patient outcomes.</p> Results <p>Baseline factors independently associated with mortality (hazard ratio (HR), 95% confidence interval (CI)) included body mass index (BMI) &lt; 18.5 (2.14, 1.17–3.91), cardiovascular disease (2.16, 1.10–4.22), advanced cancer (4.65, 1.73–12.5), impaired walking (2.33, 1.17–4.64), emergency dialysis without fistula (1.88, 1.03–3.44), fluid overload (2.70, 1.43–5.07), serum albumin &lt; 3.0&#xa0;g/dL (2.32, 1.25–4.32), and C reactive protein (CRP) &gt; 0.5&#xa0;mg/dL (3.87, 1.85–8.10). A scoring system was developed, assigning 1 point each for BMI &lt; 18.5, cardiovascular disease, impaired ambulation, emergency dialysis without fistula, fluid overload, and serum albumin &lt; 3.0&#xa0;g/dL, and 2 points for advanced cancer and CRP &gt; 0.5&#xa0;mg/dL. The score demonstrated an area under the ROC curve of 0.83. The hazard ratios for 3-year mortality for scores of 4–5 and 6 or higher, compared to 0–3, were 2.55 (95% CI: 1.04–6.23) and 7.10 (3.36–15.0), respectively (<i>P</i> for trend &lt; 0.001). Subgroup analyses confirmed the score's robustness.</p> Conclusion <p>The prognostic score for 3-year mortality in very elderly patients who initiate dialysis should be validated in different populations and&#xa0;is expected to inform decisions regarding dialysis initiation.</p> Graphical abstract <p></p>