Infection with the hepatitis C virus (HCV) has become a leading cause of scarring of the liver (i.e., fibrosis) and cirrhosis in the United States. HCV-related cirrhosis (with its associated complications, such as liver cancer) is a major cause of death, although it develops slowly and occurs only in approximately one-third of HCV-infected patients. Alcohol can exacerbate HCV infection and the associated liver damage by causing oxidative stress and promoting fibrosis, thereby accelerating disease progression to cirrhosis. Furthermore, alcohol may exacerbate the side-effects associated with current antiviral treatment of HCV infection and impair the body's immune defense against the virus. Of the HCV-infected people who do not consume alcohol, only a minority progresses to severe liver disease and requires antiviral treatment. Because alcohol potentiates the fibrosis- and cancer-inducing actions of HCV, alcoholics are particularly vulnerable to HCV infection and most in need of treatment.