*Purpose: Obesity is increasingly prevalent among candidates for kidney transplantation. Outcomes for obese patients remain uncertain, as existing studies have shown conflicting short and longer-term post-transplant outcomes. We aimed to compare graft and patient survival between obese and non-obese kidney transplant recipients, while controlling for donor characteristics by comparing recipients of paired kidneys.

*Methods: We accessed the Australia and New Zealand Dialysis and Transplant Registry and selected all transplant pairs between 2000 and 2020, where a deceased donor supplied one kidney to an obese patient and the other to a non-obese patient. We used the World Health Organisation classification of obesity as body mass index greater than 30 kg/m² for non-Asians, and greater than 25 kg/m² for Asians. We compared the incidence of delayed graft function (DGF) by conditional Poisson regression, and graft failure and death by Stratified Cox regression.

*Results: The proportion of obese patients has doubled in the past 20 years (20% in 2000 versus 42% in 2020). Of the 1,584 pairs identified, 603 (38%) obese recipients experienced DGF compared with 466 (29%) non-obese recipients. Obesity was associated with a 30% increased risk of DGF (aHR 1.30, 95% CI 1.14-1.48, p<0.01). Obese recipients were more likely to experience death-censored graft failure (aHR 1.19, 95% CI 1.00-1.43, p=0.045), and 1.3 times more likely to die prematurely with function (aHR 1.30, 95% CI 1.09-1.54, p=0.003), compared to their non-obese pair. Long-term patient survival was significantly better in non-obese recipients with 10-, 15-, 20-year survival of 78%, 63%, 53% compared to 72%, 57% and 39% in obese patients.

*Conclusions: We found that obesity was strongly associated with an increased risk of DGF and inferior long-term outcomes. Addressing obesity is an unmet clinical need in kidney transplantation.

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