When the data were stratified by the type of allergic disease, a significant association between IL-18 −137G/C polymorphism and AD was found under recessive model (CC versus CG + GG: OR = 0.30, 95% CI = 0.15–0.60, P < 0.001) and homozygous comparison (CC versus GG: OR = 0.26, 95% CI = 0.12–0.53, P < 0.001). This evidence concerns the gene IL18 and Alzheimer disease.