Background: The present study aimed to determine the frequency of the IL28B polymorphism rs8099917 in patients with genotype 1 hepatitis C virus (HCV) infection treated with pegylated-interferon-α2b (PEG-IFN-α2b) and ribavirin (RBV) and its treatment outcome. Materials and Methods: The IL28B rs8099917 genotypes were determined among 100 HCV-infected patients and the viral load was also estimated. PEG-IFN-α2b and RBV combination were administrated to the patients for 48 weeks and the treatment outcome was defined. Results: Sixty-seven (67%), 27 (27%), and 6 (6%) of 100 patients were determined as TT, GT, and GG genotype, respectively. The response rate to treatment was significantly higher in patients with TT genotype. Conclusion: According to the results of the present study, patients with IL28B rs8099917 TT genotype achieve higher sustained virological response than the GT and GG genotypes. Thus, when there are no alternatives, treatment with PEG-IFN-α2b and RBV combination can be suggested in patients with IL28B TT genotype.