Whatever the mechanism, a clear correlation between HLA-A-Bw4 alleles and susceptibility to encephalitis was reported in our study, pointing out the need for further investigations also on the variability of this KIR gene, aiming to improve the predictive value of the possible combined variable KIR3DL1/HLA-A-Bw4. The gene discussed is KIR3DL1; the disease is encephalitis.