Abstract Objective: Kidney transplantation (KT) procedures are confronted with adverse outcomes that include allograft failure. Allograft survival are in large part attributed to genetics, which render the recipient susceptible or protected from allograft rejection. The genetics of KT outcomes point to single nucleotide polymorphisms (SNPs) where studies have reported the role of cytokines in allograft survival, one of which is interleukin-18 (IL-18). Reported associations of IL-18 with KT outcomes have been inconsistent. This prompted a meta-analysis to obtain more precise estimates. Methods: From four included articles, we posed two hypotheses about IL-18 SNPs: (1) they are either high in patients (hp) /controls (hc) based on genotype distribution (GD) and (2) they either increase or decrease the risks of allograft rejection. To this end, we compared the IL-18 genotypes to estimate odds ratios [ORs] and 95% confidence intervals using standard genetic models (homozygous, recessive, dominant and codominant). Subgrouping was ethnicity-based. Heterogeneous (random-effects) associations were subjected to outlier treatment which split the outcomes as pre- (PRO) and post- (PSO) outlier. Stability and robustness of the outcomes were analyzed by Bonferroni-correction and sensitivity treatment, respectively.Results: Our results revealed two core outcomes based on significance (Pa < 0.05): (1) genotype frequency was hp than hc (OR 1.34, Pa = 0.0007) in the codominant model (PSO) based on stability and robustness and (2) protection from allograft rejection (OR 0.74, Pa = 0.04) in the dominant model (PRO) based on homogeneity. Subgroup analysis showed that Caucasian and Asian outcomes validated the GD and allograft outcomes, respectively. Conclusions: The IL-18 SNPs showed associations (hp) with KT up to 1.3-fold and protected KT recipients from allograft rejection (26%). Subgroup outcomes delineated the Asian and Caucasian effects. Enabled by outlier treatment, these findings were supported by non-heterogeneity. More studies should confirm or counter our findings.