The prevalence of hepatitis C virus (HCV) infection varies in different populations, ranging from as low as 0.6% in volunteer blood donors to as high as 80% in injection drug users. The prevalence of HCV in a population can be predicted by risk factors associated with the transmission of infection. These risk factors include injection drug use, blood product transfusion, organ transplantation, hemodialysis, occupational injury, sexual transmission, and vertical transmission. We review the literature regarding the incidence and prevalence of HCV infection and the evidence supporting various modes of HCV transmission.