Infection with the hepatitis C virus leads to chronic hepatitis in the majority of patients. Diagnosis is based on the presence of anti-HCV antibodies and confirmed by positive HCV RNA. The natural course of the disease is slow. Cirrhosis is found in a minority of patients two decades post infection. Nevertheless, cirrhosis is much more frequently observed than in patients with hepatitis B infection. Treatment of choice is interferon-alpha. Today combination with ribavirin is recommended for most patients. In combination therapy the sustained response rate six months after stop of treatment is about 40% in naive patients with respect to virus elimination. In patients treated with high doses of interferon-a for one year the sustained response rate is comparable. The response rate is higher in patients with HCV infections of non-1 genotype and in patients with lower virus titers, e.g. less than 2 Mill. genome equivalents per ml. Interferon-a treatment also leads to an improvement of liver histology. Necro-inflammatory scores are reduced. It has also an antifibrogenic effect. Progression of fibrosis is reduced. The antiproliferative effect of interferon-a leads a lower rate of hepatocellular carcinomas, which has been demonstrated in several retrospective studies. In patients with Child A cirrhosis the time till decompensation is delayed. Because of the slow progression, the relatively low response rate and the adverse events of interferon-a and ribavirin treatment should be instituted on an individual base depending on host factors such as age, co-morbidity and stage of liver disease.