Hepatitis C virus (HCV) infection causes liver disease. A person gets HCV infection from contact with the blood of someone with HCV infection. Before routine HCV testing of donated blood began in 1990, many people got HCV infection from blood transfusions. Other risk factors for HCV infection include kidney dialysis, being the child of a mother with HCV infection, sexual contact with a person with HCV infection, illicit drug use, and contact with blood in the workplace (such as might occur in health care workers). However, the source of infection is unknown in many people. Although some people with HCV infection need liver transplants or die, many have no symptoms and never develop liver disease. About 2 out of every 100 U.S. adults have HCV infection, but many people who are infected do not know that they are. Blood tests can identify whether a person has HCV infection. Drugs are available to treat HCV infection, but they can cause side effects, are only partly effective, and are expensive. Screening for HCV would involve testing healthy people for HCV infection so that they could begin treatment before symptoms develop. Screening makes sense only if the benefits of treating HCV infection before symptoms develop are greater than the potential harms.