Currently seven viruses, A, B, C, D, E, G and transfusion transmitted virus (TTV), are recognised in the hepatitis virus alphabet. Hepatitis G virus and TTV probably do not cause liver disease in humans. Hepatitis A and E usually cause a self-limiting hepatitis followed by complete recovery but occasionally cause fulminant hepatic failure. Hepatitis B and C are major public health problems worldwide due to their sequelae of chronic hepatitis, cirrhosis and primary liver cancer. Chronic hepatitis C is a particular health issue for Western Europe already, accounting for 40% of end-stage cirrhosis and 30% of liver transplants. The contribution of hepatitis C to chronic liver disease is predicted to rise in the future. Vaccines can prevent hepatitis A and B. Interferon alpha is effective treatment in 25-30% of patients with chronic hepatitis B or C. The prospects for treating chronic hepatitis B have been improved by the introduction of reverse transcriptase inhibitors. Lamivudine is the first drug of this class to be licensed. The optimal use of these new drugs is currently being studied. The success rate for treating chronic hepatitis C can be raised to about 40% with combination therapy of interferon alpha and ribavirin. A large research effort to discover new antiviral agents against hepatitis C is already giving the prospect of more effective therapies in the next few years.