Hepatitis C virus (HCV) infection is a major cause of chronic liver disease and associated complications such as liver cirrhosis and hepatocellular carcinoma (HCC). Viral and host factors are known to be predictors for antiviral therapy. Host factors that are predictors of sustained viral response (SVR) were discovered by genome-wide association studies (GWAS), including single-nucleotide polymorphisms (SNPs) in or near the interferon lambda gene (rs8099917, rs12979860 and rs368234815). The aim of the present study was to verify the genotype frequencies of SNPs rs8099917, rs12979860 and rs368234815 and to evaluate the association between SNPs and the outcome of HCV infection, taking into account the population ancestry. In this study, there was an association of the three polymorphisms with both clinical outcome and response to treatment with PEG-IFN and RBV. The polymorphisms rs12979860 and rs368234815 were associated with increased sensitivity (97.7 %, 95 % CI 87.2-100, and 93.3 %, 95 % CI 81.3-98.3; respectively) and with a greater predictive value of a positive response to treatment. In multivariable analysis adjusted by gender, age and ancestry, the haplotype G/T/ΔG was related to non-response to treatment (OR = 21.09, 95 % CI 5.33-83.51; p < 0.001) and to a higher chance of developing chronic infection (OR = 5.46, 95 % CI 2.06-14.46; p = 0.001) when compared to the haplotype T/C/TT. These findings may help to adjust our treatment policies for HCV infection based on greater certainty in studies with populations with such genetic characteristics, as well as allowing us to get to know the genetic profile of our population for these polymorphisms.