We assessed the impact of the one-year endourological society fellowship program (ESFP) on the achievement of optimal surgical outcomes (OSO) in stone patients treated with ureteroscopy (URS). We identified 303 stone patients treated with URS from January 2018 to June 2022 by five experienced surgeons (ES). Of those, two attended ESFP. OSO was defined as the presence of residual fragments ≤ 4mm at 1-month post-operative imaging (Ultrasound + X - Ray or CT scan). Descriptive statistics explored patients' characteristics and the rate of OSO according to the attendance of ESFP. Uni- and multivariate logistic regression analyses (UVA and MVA) tested the impact of stone characteristics, surgical data, ESFP, and imaging technique on the rate of OSO. The LOWESS curve explored the graphical association between stone size and the multivariable-adjusted probability of OSO in the two groups of surgeons. Of 303 patients, 208 (69%) were treated by the two surgeons who attended ESFP. OSO was achieved in 66% and 52% of patients treated by ES with and without ESFP, respectively (p = 0.01). At UVA, ESFP (OR = 1.78; 95% CI = 1.09-2.90), stone diameter (OR = 0.92; 95% CI = 0.88-0.96), stone location (kidney vs. ureter; OR = 0.34; 95% CI = 0.21-0.58), imaging technique (CT scan vs. Ultrasound + X-Ray; OR = 0.28; 95% CI = 0.16-0.47) predicted OSO achievement (all p < 0.05). At MVA analyses, ESFP was associated with OSO (OR = 2.24; 95% CI = 1.29-3.88; p < 0.05), along with the other aforementioned variables. The LOWESS curve showed that the greater the stone size, the greater the difference in OSO in the two groups of surgeons. ESFP positively affects OSO achievement after URS, especially in patients with a high stone burden.