This is a Phase I, open-label trial to investigate the single-dose pharmacokinetics of telaprevir (TVR) in 12 participants with severe renal impairment (defined as creatinine clearance (CrCl) < 30 mL/min) as compared to 12 participants with normal renal function, matched for sex, race, age (± 10 years) and BMI (± 20%). Open-label means that the study doctor and the participants know what treatment will be assigned to them. All participants will receive a single 750-mg dose of TVR. Pharmacokinetic profiles of total TVR up to 24 hours postdose will be determined. A 24 hour urine collection test will be performed to estimate the CrCl. In addition, the effect of severe renal impairment on the total and unbound plasma concentrations of the sum of TVR and VRT-127394 will be assessed. Tolerability and safety of TVR will be assessed throughout the trial period. Illnesses and side effects will be checked at every visit. Blood and urine samples will be taken at screening, on Day 1, 2 and at the 2 follow-up visits. ECG and vital signs will be taken at screening, twice on day 1, on day 2 and at the first follow-up visit. At the second follow-up visit vital signs alone will be determined. A physical examination will be done at screening, on the day before TVR intake, on day 2 and at both follow-up visits. All participants will receive a single 750-mg dose of telaprevir (TVR) given by mouth as 2 tablets of 375 mg.