The paper reviews the available information on the newly discovered viruses originally supposed to cause post-transfusion hepatitis. GBV-C/Hepatitis G virus belongs to the Flaviviridae family, and can be transmitted parenterally like Hepatitis C virus. Its role in causing hepatitis or other diseases has not been proved yet. The other newly discovered viruses contain single-stranded circular DNA, with a wide range of sequence divergence. These viruses can be transmitted not only with blood and blood products but via fecal-oral route as well. They are unique among enterally transmitted viruses in the sense that the virus persists for years in the human body, therefore their genomes may be detected in the blood of the healthy population in high percentage. One of the genotypes of TTV is suspected to cause hepatitis. High TT virus load was found as an independent factor associated with the occurrence of hepatocellular carcinoma among patients with hepatitis C virus-related chronic liver disease. It is not clear yet, whether TTV-like minivirus and SEN virus cause any illnesses.