Background: Adipose tissue might affect response to immune checkpoint inhibitors (CPI) in cancer patients (pts). Higher BMI is associated with improved outcomes in mRCC under VEGFR TKI but BMI impact under CPI remains unclear. Methods: We analysed BMI in the NIVOREN GETUG AFU 26 study, a prospective study that evaluated the safety and efficacy of nivolumab in mRCC after failure of prior VEGFR inhibitors. We investigated the association between BMI, objective response rate (ORR), progression-free survival (PFS), and overall survival (OS). BMI (weight/height ²⁾ was classified according to the World Health Organization (WHO) categories: underweight as BMI < 18.5; normal weight as 18.5 ≤ BMI ≤ 24.9; overweight as 25 ≤ BMI ≤ 29.9 and obesity as BMI ≥ 30. Survival distributions were compared using a Log-Rank test, supported by uni- and multivariate Cox regressions to estimate the Hazard Ratio (HR) and its 95% CIs. Median follow-up (FU) and the 95% CI were calculated using the reverse Kaplan–Meier method. Results: Overall, 708 pts were included in the BMI analysis: 20 pts (2.8%) were underweight, 322(45.5%) had normal weight, 255(36.0%) were overweight and 111(15.7%) obese. Median age was 64 years, 77.3% were male, performance status was ≥ 80% in 81.2%, and IMDC risk group was good, intermediate and poor in respectively 18.2%, 56.4%, 25.4%. Outcomes according to BMI is detailed in table, median FU was 23.9 months (95%CI 23.0-24.5). BMI adjusted to known prognostic factors was not significant in the multivariate analysis. Conclusions: Higher BMI patients seems to have better outcomes with nivolumab in mRCC. Further characterisation is on-going to explore the relation of BMI with established risk factor in pts under CPI in mRCC.