BACKGROUND TTV is a newly discovered virus and little is known about the frequency of TTV infection in children in Poland. The aim of our study was to investigate the frequency of TTV infection in children with chronic viral hepatitis B and C. MATERIAL/METHODS Two patient groups were tested: 74 patients with chronic hepatitis B aged 4 to 20 years, and 13 patients with chronic hepatitis C aged 10 to 18 years. Nucleic acids were extracted from serum using the spin column technique (QIAGEN(r), Hilden, Germany), and TTV DNA sequences were amplified by nested PCR. RESULTS TTV DNA was found in 47.3% of patients with chronic hepatitis B and in 53.8% of patients with hepatitis C. Among those patients with chronic B hepatitis there was no statistical difference between the frequency of coinfection with TTV and clinical-histopathological diagnosis, activity of aminotransaminases, frequency of seroconversion of HBeAg to antiHBe, or interferon alpha therapy. CONCLUSIONS In Poland, TTV viremia is frequent in patients with chronic viral hepatitis B and C. TTV coinfection did not modify the course and activity of chronic hepatitis B or influence the outcome of interferon therapy.