BACKGROUND: Long-term outcomes remain heterogeneous for patients with discrete membranous subaortic stenosis who underwent surgical repair. We aim to develop and validate an extended risk model for predicting secondary surgery following repair of discrete membranous subaortic stenosis in pediatric patients. METHODS: We retrospectively analyzed 235 children undergoing discrete membranous subaortic stenosis repair between 2008 and 2023. The primary end point was secondary surgery for significant aortic regurgitation or recurrent left ventricular outflow tract obstruction. Building on our previously published model, we evaluated additional clinical and hemodynamic predictors and assessed model performance using discrimination, calibration, and reclassification metrics. Internal validation was performed using bootstrap resampling and temporal sensitivity analyses adjusted for surgical era. RESULTS: During a median follow-up of 6.0 years, 25 patients (10.6%) required secondary surgery. The original Dong model demonstrated excellent discrimination (C-index 0.93). Incorporation of age <5 years and preoperative left ventricular outflow tract gradient significantly improved predictive performance (C-index 0.95) and risk reclassification at 5 and 10 years (net reclassification improvement 0.75 and 0.64, respectively). A nomogram-derived score (cutoff 32.0 points) stratified patients into low-risk (n=170) and high-risk (n=65) groups with marked separation. Risk accumulation was most pronounced between 5 and 10 years after initial repair, and findings were robust after adjustment for surgical era. CONCLUSIONS: An extended risk model integrating clinical, anatomic, and hemodynamic variables accurately predicts secondary surgery after discrete membranous subaortic stenosis repair. This approach enables individualized postoperative surveillance, particularly intensified monitoring during the 5- to 10-year high-risk window and supports timely reintervention planning.