Abstract Background The access of obese patients to kidney transplantation is limited despite several studies showing that obese transplant recipients had a better survival rate than those undergoing dialysis. The aim of this study was to compare patient and graft survival rates and post-renal transplant complications in obese patients and non-obese patients and to assess the effect of pre-transplant weight loss in obese patients on transplant outcomes. Methods We carried out a prospective cohort study using two French registries REIN and CRISTAL on 7 270 kidney transplant patients between 2008 and 2014 in France. We compared obese patients with non-obese patients and obese patients who lost more than 10% of weight before the transplant (Obese WL and Obese nWL). Results The mean BMI in our obese patients was 32 kg/m2. Graft survival was lower in obese patients than in non-obese patients (HR = 1.40, IC 95% [1.09; 1.78], P = 0.007) whereas patient survival was similar (HR = 0.94, IC 95% [0.73; 1.23], P = 0.66). Graft survival was significantly lower in Obese WL than in Obese nWL (HR = 2.17, CI 95% [1.02; 4.63], P = 0.045) whereas patient survival was similar in the two groups (HR = 0.79, IC 95% [0.35; 1.77], P = 0.56). Conclusion Grade I obesity does not seem to be a risk factor for excess mortality after kidney transplantation and should not be an obstacle to having access to a graft. Weight loss before a kidney transplant in this patients should not be essential for registration on waiting list.