The KIR AA plus Bw4 compound genotype was more frequent in healthy individuals (42.4%) than in subjects with ALL (30.2% adult, p = 0.0002, and 31.0% pediatric p = 0.011) or AML (34.8% adult, p = 0.017 and 32.5% pediatric, ns). This evidence concerns the gene KIR3DL1 and acute lymphoblastic leukemia.