Hepatitis C virus (HCV) was discovered in 1989. HCV is a positive single-strand RNA. We all have thought, that HCV can replicate only in liver tissue, but now we know, that HCV can replicate in extrahepatic tissue as well. In about 48-86% of HCV infected patients, chronic hepatitis C (CHC) has been noticed and eventually, after tens of years, liver insufficiency, cirrhosis or hepatocellular carcinoma. The current recommended treatment for CHC is a combination of pegylated-interferon alpha and Ribavirin. Presently it is known, that HCV infection can persist as an occult infection. RNA HCV can be detected in patients after successful treatment for CHC or spontaneous elimination. Persistent HCV replication in hepatocytes or lymphoid cells would likely lead to continuous antigenic stimulation of the immune system. This prolonged replication may contribute to the immune tolerance of HCV, impairment of immune response and even further virus persistence. This occult infection grows more important in transplantation.