The 2'-5'-oligoadenylate synthetase (2'-5'-OAS) family members are interferon-induced antiviral proteins. Twenty-three single nucleotide polymorphisms located within the OAS1, OAS2, OAS3, and OASL genes were analyzed in 142 patients with Russian tick-borne encephalitis. Statistically significant differences in genotype, allele, and haplotype frequencies for 3 OAS2 single nucleotide polymorphisms (rs1293762, rs15895, and rs1732778) and 2 OAS3 single nucleotide polymorphisms (rs2285932 and rs2072136) were detected between patients with central nervous system disease and both those with fever and/or meningitis and the control group. The data suggest a possible association between these 5 OAS single nucleotide polymorphisms and the outcome of tick-borne encephalitis virus infection in a Russian population.