Recent advances in our understanding of viral hepatitis involve the discovery and further characterization of the hepatitis C virus and the interferon treatment of patients with chronic viral hepatitis. Liver cirrhosis and primary hepatocellular carcinoma can develop after some years of disease. Interferon is the only effective treatment, which may improve symptoms and prognosis in some patients. Long-term responses with termination of viral replication are seen in 40% of patients with hepatitis B and 15-25% of patients with hepatitis C. In some patients complete elimination of the virus occurs. Higher response rates are achievable in subgroups of patients with favourable prognostic constellations. Patients have to be informed about side-effects and risks of interferon therapy. Treatment in uncomplicated cases is performed on an outpatient basis. The present paper reviews diagnosis, indications, contraindications and practical considerations concerning interferon treatment in patients with chronic viral hepatitis.