After liver transplantation (LT) for hepatitis C virus (HCV)-related cirrhosis, recurrence of HCV infection is universal. The efficacy of antiviral therapy in this indication is usually reduced because of its poor tolerability. We present herein the results of plasma measurement of ribavirin levels in transplanted patients when using increasing dosage of ribavirin, in comparison with a control cohort of nontransplanted patients. Seventeen control patients (nine women and eight men, median age 51.5 years) were compared with 12 liver transplant patients (2 women and 10 men, median age 55 years). In 76% of patients, HCV infection was genotype 1. All patients were treated by a combination of ribavirin and pegylated-interferon α-2b. A total of 54 blood samples were taken (1.8 per patient) for ribavirin level measurement. A virological response was obtained in 8/17 patients in the control group and in 6/12 LT patients. Ribavirin dose was lower in the LT group (8.79 vs 12.98 mg/kg/day), but plasma levels were the same in both groups (2.23 vs 2.43 mg/L for LT and non-LT groups, respectively). This was probably related to impaired renal function in the LT group (serum creatinine: 112.6 vs 73.6 μmol/L). No discontinuation of ribavirin therapy was observed and haemoglobin level was the same in both groups (109.5 g/L in LT patients vs 119.5 g/L in the control group). These results strongly support the interest in plasma measurement of ribavirin concentration during antiviral therapy in LT patients. Ribavirin dosage might be adapted without compromising its efficacy.