PIP: Hepatitis C refers to the portion of non-A, non-B hepatitis that is parenterally transmitted. No formal classification of the virus has yet been achieved, but it is known to be heterogeneous, a trait with implications for both antiviral therapy and vaccine development. Hepatitis C virus has a nearly uniform distribution around the world. The highest infection rates are found in patients with non-A, non-B hepatitis associated with transfusion, hemophiliacs receiving coagulation factors, intravenous drug users, and renal dialysis patients. Screening for hepatitis C, even using third generation ELISA tests, has not completely eliminated risk of transmission during blood transfusions. Nonpercutaneous routes of transmission have been poorly defined. There is evidence that hepatitis C virus is sexually transmitted, but less efficiently than hepatitis B or HIV. Hepatitis C infections have been found in newborns and in children receiving transfusions, undergoing renal dialysis, or hospitalized. The high percentage of hepatitis C in persons with no history of parenteral exposure has stimulated search for nonparenteral forms of transmission, especially vertical transmission. The resulting data have been contradictory. Results of recent studies using polymerase chain reaction appear to indicate that perinatal transmission occurs, but an elevated viral load of hepatitis C is required to produce infection. The majority of hepatitis C cases are asymptomatic. Normal serum aminotransferase levels may mask persistent infection and progression to cirrhosis. More serious consequences of chronic infection may include persistent acute or chronic hepatitis, with cirrhosis developing in 20-30% of cases, and hepatocellular carcinoma. The most effective treatment of chronic infection, alpha interferon, is associated with a relapse rate of 80-90%. Prevention is thus the most effective intervention to combat hepatitis C.