KCNJ11 polymorphisms have been linked to the risk of developing type 2 diabetes. Our aim was to define the contribution of KCNJ11 to new-onset diabetes after transplantation (NODAT) among patients treated with Tacrolimus (Tac). A total of 115 NODAT and 205 non-NODAT were genotyped for rs5219 (p.E23K). AA + AG genotypes were significantly associated with NODAT-risk (p = 0.004; OR = 2.10). The reported effect of this KCNJ11 polymorphism on insulin release by beta cells could explain this association.