This is an open-label, single-arm study of sofosbuvir (GS-7977) and ribavirin (RBV) in adults who have had a liver transplant which has become re-infected with hepatitis C. The treatment period is 24 weeks with up to 48 weeks of follow up. The total time in this study will last up to 72 weeks not including the screening visit.

Inclusion Criteria:

• Subjects with evidence of chronic HCV (all genotypes) documented pretransplantation
• HCV RNA ≥ 10,000 IU/mL at screening
• Absence of organ rejection as documented by post transplant liver biopsy taken no more than 12 months prior to baseline/Day 1 visit
• Liver transplant ≥ 6 months and ≤ 12 years prior to screening
• Naive to all nucleotide/nucleoside treatments for chronic HCV infection

Exclusion Criteria:

• Multiorgan transplant that includes heart or lung recipient
• Subjects with de novo or recurrent Hepatocellular Carcinoma(HCC) post transplant
• Current use of corticosteroids at any dose > 5mg of prednisone/day (or equivalent dose of corticosteroid)
• Infection with hepatitis B virus (HBV) or HIV at screening
• Current, uncontrolled ascites, variceal hemorrhage, hepatic encephalopathy, hepatorenal syndrome, hepatopulmonary syndrome, or other signs of decompensated cirrhosis