HCV infection is a common cause of liver disease in both patients undergoing organ transplantation and the post-transplant period. Increasingly sensitive and specific techniques to diagnose this infection have enabled us to understand the relationship between pretransplant and post-transplant infection and to study the consequences of infection in these immunocompromised patients. The use of anti-HCV-positive organ donors is highly controversial and will remain so until the natural history of post-transplant HCV infection is known. Study of the relationship between histological damage and level of HCV replication will likely provide insights into the biology of this virus and mechanisms of hepatic damage.