Limited magnetic resonance imaging (MRI) data on autograft dilatation following the Ross procedure in congenital cohorts presents challenges in understanding its evolution and impact on clinical outcomes. This study, spanning from February 2003 to December 2022, included patients under 40 years at the time of the Ross procedure, with MRI follow-ups assessing dimensions at key aortic sites. Among 307 patients, 132 MRIs were analyzed from 76 individuals, revealing that autograft z-scores increase primarily with time post-procedure (Coef. 0.13; 95% CI:0.051-0.216; P = 0.002). Additionally, older patients at the time of surgery showed larger ascending aortic dimensions (Coef. 0.13; 95% CI:0.099-0.165; P = 0.001). Notably, autograft dilation at the sinus of Valsalva significantly predicted higher reintervention risks (HR 1.57; 95% CI:1.21-2.04; P = 0.001). Surgical reinforcement techniques of the autograft, via subcoronary implantation or external support, prevented such dilation (P < 0.001) and mitigated aortic regurgitation. In conclusion, our model predicted autograft dilation over time in patients after Ross procedure, aiding clinicians in making data-driven decisions regarding the optimal timing of the procedure and the selection of the most effective surgical strategy.