Hepatitis C virus commonly causes chronic liver disease. Chronicity as a result of the failure of T-cell-mediated immunity, liver damage caused by cytotoxic T lymphocytes, and the evolution of genetic diversity characterize hepatitis C infection. Progression, typically silent, is determined by sex, age, alcohol and immune status. Interferon and ribavirin are effective in the substantial minority of patients with less advanced fibrosis and lower hepatitis C viral loads.