The risk of severe anemia is increased in patients treated by tri-therapy compared to patients treated by bitherapy. The underlying mechanisms involved in this toxicity remain unexplored but could also depend on the global exposure of telaprevir. The trough concentration or AUC of telaprevir could therefore be a predictive factor of the onset of anemia in patients treated by ribavirin/PEG-INF/telaprevir. The early measurement of telaprevir and ribavirin concentrations could help to manage HCV tri-therapy to improve tolerance and SVR.