Observational follow-up study to assess long-term response to telaprevir and to evaluate changes in Hepatitis C virus over time.

Inclusion Criteria:

• Received at least 1 dose of telaprevir-based treatment in 1 of the following clinical studies: VX05-950-104, VX05-950-104EU, VX06-950-106, VX06-950-107, VX07-950-108, VX08-950-111, or VX-950-TiDP24-C216
• Have baseline HCV viral sequencing data available from previous telaprevir study

Exclusion Criteria:

• May not be currently participating in the antiviral follow-up period of an ongoing telaprevir trial. (Note: Subjects who have completed the required antiviral follow-up period but are still participating in the collection of patient-reported outcomes data for their previous telaprevir study may be eligible.)
• For subjects participating in ongoing studies at the time of enrollment, have more than 90 elapsed days between the database lock or unblinding in the previous telaprevir study and Day 1 in this study

Subjects who have previously received at least 1 dose of telaprevir-based treatment (telaprevir plus peginterferon alfa 2a [Peg IFN-alfa-2a] with or without ribavirin [RBV]) in 1 of the following clinical studies: VX05-950-104, VX05 950-104EU, VX06-950-106, VX06-950-107, VX07-950-108, VX08-950-111, and VX-950-TiDP24-C216.