After liver transplantation (LT), the management of recurrent hepatitis C virus (HCV) infections still remains a major challenge. In HCV genotype 1 patients not undergoing transplantation, the introduction of protease inhibitor (PI)–based regimens has increased the sustained virological response rate significantly. This pilot study investigated both the safety and efficacy of telaprevir (TVR)-based triple therapy in HCV-infected LT patients with a special emphasis on drug-drug interactions between immunosuppressants and PIs. Safety and efficacy data were gathered for 12 weeks for 9 HCV-infected LT patients who were treated with a combination of TVR, pegylated interferon, and ribavirin (RBV) in parallel with immunosuppressive drugs such as tacrolimus (TAC; n = 4), cyclosporine A (CSA; n = 4), and sirolimus (SIR; n = 1). Seven of the transplant patients completed the 12 weeks of triple therapy. At week 4, 4 of the patients were found to be HCV RNA–negative, and importantly, 8 were found to be negative at week 12. During the 12-week course of triple therapy, short-term measurements of immunosuppressant trough levels required individual dose reductions in all patients (CSA, 2.5-fold; SIR, 7-fold; and TAC, 22-fold). Furthermore, two-thirds of the patients exhibited hematological side effects requiring RBV dose reductions, the administration of erythropoietin, or even blood transfusions. In conclusion, this pilot study provides evidence showing that TVR-based triple therapy is effective within the first 4 to 12 weeks in LT patients suffering from HCV genotype 1 recurrence, and it also provides evidence showing that drug-drug interactions between TVR and immunosuppressants can be handled appropriately through the close monitoring of trough levels and adequate dosage adjustments. Liver Transpl, 2012. © 2012 AASLD.