The hepatitis C virus (HCV) infects nearly 170 million people worldwide and is responsible for approximately 20% of cases of acute hepatitis and 70% of cases of chronic hepatitis. Acute hepatitis is icteric in only 20% of patients and is rarely severe. Eighty-five percent of infected patients develop chronic infection which is generally asymptomatic, resulting in most cases in fortuitous diagnosis, which may be made at a late stage. Twenty-five percent of the HCV chronic carriers have persistently normal serum alanine aminotransferase (ALT) levels despite having detectable HCV RNA in serum; 75% have elevated ALT levels. The former patients usually have mild histologic lesions, probably with a good long-term prognosis. In the latter patients, a liver biopsy is the most accurate way to distinguish patients with mild chronic hepatitis from those with moderate or severe chronic hepatitis. While most patients with mild chronic hepatitis have a slowly progressive liver disease, the patients with moderate or severe chronic hepatitis may develop cirrhosis within a few years. In patients with HCV-related cirrhosis, the incidence of hepatocellular carcinoma is 2-5% per year. At presently, HCV-related end-stage cirrhosis is the first cause of liver transplantation.