Some single nucleotide polymorphisms (SNPs) of the gene encoding interleukin 28B (IL28B) may increase susceptibility to infection and chronicity in humans with hepatitis B and C viruses. In our study, we aimed to investigate the prevalence of rs12979860, rs8099917 and rs12980275 SNPs in IL28B in patients with hepatitis B (HBV) or hepatitis C Virus (HCV) infection and to determine the relationship of these polymorphisms with plasma IL28B levels. For this purpose, 64 HBV-infected and 66 HCV-infected patients and 70 healthy individuals were included in the study. The SNPs were investigated by real time PCR (Polimerase Chain Reaction, Rt-PCR) using TaqMan SNP Genotyping Assay. The plasma levels of IL28B were detected by 'Enzyme Linked Immunosorbent Assay (ELISA)'. The frequencies of the rs12980275AG genotype and G allele (p= 0.003 and p= 0.04, respectively), and the rs12979860CT genotype and T allele (p= 0.01 and p= 0.04, respectively) were lower in HBV-infected patients. In HCV-infected patients, the rs8099917TG genotype and G allele frequencies (p= 0.04) were higher and the TGG haplotype showed a statistically significant difference (p= 0.04). The mean of IL28B plasma levels were higher in the control group than the HBV or HCV-infected patient groups (p= 0.001 and p= 0.01, respectively). However, HBV-infected patients with the rs12980275AG genotype showed a significant difference in plasma IL28B levels compared to the other genotypes (p= 0.0001) and these patients had lower viral loads (<105 IU/ml). According to the results of the study, it can be stated that rs12979860CT and rs12980275AG genotypes may play a role in preventing the chronicity of HBV infection, while rs8099917TG genotype may contribute to the transformation of HCV infection into chronic infection. In this study, it was observed that the presence of the G allele for the rs8099917 polymorphism could be evaluated as a risk allele for chronic HCV infection and that the TGG haplotype could have a strong predictive effect on increasing susceptibility to chronic HCV infection. It is recommended to evaluate the genotypic distribution of IL28B before treatment because of its prognostic significance in HBV or HCV infected patients. In HBV infection, the rs12980275AG genotype which is thought to have a protective effect by limiting viral replication with increased plasma IL28B levels, can be used as a good prognostic factor. These polymorphisms could be used as biomarkers to predict the clinical consequences of the patients infected with HBV or HCV, to take precautions to prevent the chronicity of the infection and its complications, and to develop new molecular targeted therapies with further research.