Although the incidence of newly acquired acute hepatitis C virus (HCV) infection has declined, an estimated 3.9 million Americans are chronically infected with HCV, most of whom are young adults who will be at risk of the severe consequences of their infection in the next 10 to 20 years. The relative importance of the two most common exposures associated with the transmission of HCV has changed over time. Blood transfusions, which account for a substantial proportion of HCV infections acquired more than 10 years ago, account for only a small portion of recently acquired infections. In contrast, injection drug use has accounted for a substantial portion of HCV infections during both the remote and recent past. Sexual exposures, which have been poorly ascertained particularly among patients with chronic hepatitis C, may account for 10% to 20% of HCV transmissions. Physicians and other health care professionals need to be educated not only about the appropriate medical management of HCV infected patients, but also about the known and potential risks for HCV infection, the need to ascertain complete risk behavior histories from their patients, the appropriate evaluation of high-risk patients for evidence of infections, and the recommendations for prevention.