Of the large number of patients chronically infected with hepatitis C virus (HCV), only about one third have progressive liver disease, and will eventually develop cirrhosis and hepatocellular carcinoma. These are the patients for whom effective antiviral treatment is most needed. Therapy is currently recommended for patients with chronic hepatitis C who have abnormal alanine aminotransferase (ALT) levels, detectable hepatitis C virus ribonucleic acid (HCV RNA) in the blood, and significant necroinflammatory changes and/or fibrosis on liver biopsy. The current gold standard in terms of treatment efficacy is the combination of peginterferon (PEG-IFN) and ribavirin. The overall sustained virological response rate (SVR) with these regimens is 54 to 61% following 48 weeks of therapy. Patients with genotype 1 infection have a 42 to 51% likelihood of response to 48 weeks of therapy. Those with genotypes 2 or 3 infection will respond to 24 weeks of therapy in 78 to 82% of cases. These SVR rates are 5 to 10 percentage points higher in all patient groups than in those obtained with standard doses of interferon (IFN) and ribavirin. Retreatment of nonresponders to standard IFN monotherapy using PEG-IFN and ribavirin has achieved SVR rates of 34 to 40%. Retreatment of patients who relapsed after IFN monotherapy has resulted in an SVR rate of about 60%. A SVR after retreatment of relapsers and nonresponders with PEG-IFN and ribavirin is more likely in patients previously treated with IFN monotherapy, those with HCV genotypes 2 or 3, patients with low viral load (<2 million copies/mL), and individuals who had a significant decrease in HCV RNA levels during the initial treatment. The potential benefits of long-term anti-HCV suppressive therapy in nonresponders are currently under investigation.