Background: The use of pegylated interferon alpha andribavirin (PegIFN/RBV) for the retreatment of chronichepatitis C virus (HCV) infection without a sustainedvirological response (SVR) prior to PegIFN/RBV treat- ment has resulted in low success rates.Aims: To investigate the efficacy and safety of telaprevir(TVR) in combination with PegIFN/RBV in patients in- fected with HCV genotypes 1 and 4 who were previous- ly treated with PegIFN/RBV and failed to achieve SVR.Study Design: Multi-center, retrospective, cross-sec- tional study. Methods: The study included 111 patients: 80 prior re- lapsers, 25 prior null responders, and six prior partial re- sponders to PegIFN/RBV treatment. The patients weregiven TVR/PegIFN/RBV for 12 weeks, followed by a12-week PegIFN/RBV treatment; virological responseresults were assessed at weeks 4, 12, and 24. Treatmentwas discontinued in patients with HCV RNA >1000 IU/ mL at week 4 or with negative RNA results at week 4 but>1000 IU/mL at week 12. Rapid virological response(RVR), early virological response (EVR), extended rap- id virological response (eRVR), and virological responseat 24th week of treatment were evaluated. The side ef- fects of combination therapy and the rates of treatmentdiscontinuation were investigated. Results: The mean age of the patients was 56.02±9.96years and 45.9% were male. Ninety-one percent of thepatients were infected with viral genotype 1, 69.6% withthe interleukin (IL) 28B genotype CT and 20.2% werecirrhotic. The RVR rate was 86.3% in prior relapsers,56% in prior null responders, and 50% in prior partialresponders (p=0.002). EVR rates in those groups were91.3%, 56%, and 83.3%, respectively (p<0.001). eRVRrates were 83.8% in prior relapsers, 48% in prior null re- sponders, and 50% in prior partial responders (<0.001).The virological response at the 24th week of treatmentwas found to be the highest in prior relapsers (88.8%);it was 56% in prior null responders and 66.7% in priorpartial responders (p<0.001). Common side effects werefatigue, headache, anorexia, malaise, anemia, pruritus,dry skin, rash, dyspepsia, nausea, pyrexia, stomachache,and anorectal discomfort. All treatments were discontin- ued due to side effects in 9.9% of patients. Conclusion: High virological response rates were ob- tained with TVR/PegIFN/RBV treatment. Although sideeffects were frequently observed, the discontinuationrate of combination therapy was low.