Herpes zoster (HZ) is induced by diseases or medical treatments leading to a decrease in cell-mediated immunity, but in most cases it appears without any detectable, predisposing condition. We report here that susceptibility to HZ is genetically determined. The promoter region of the IL-10 gene contains 3 single-nucleotide polymorphisms (G/A at -1082, C/T at -819 and C/A at -592) which form 3 haplotypes, GCC, ACC and ATA. These haplotypes are known to differ in terms of their effect on the transcription of the IL-10 gene. In a cohort of 60 HZV patients, the number of carriers of the ATA haplotype was 32 (53%), while in blood donors the frequency was 151/400 (38%) (p < 0.05).