Background/Aims: A novel DNA virus which was designated TT virus (TTV) in 1997 was considered a possible hepatitis-related virus, like hepatitis C (HCV), hepatitis B (HBV) and GB virus C/hepatitis G viruses (GBV-C/HGV). In the present study, the molecular epidemiology and clinical significance of TTV, GBV-C/HGV and HCV infection in hemodialysis patients from Taiwan are investigated. Methods: Sera of 85 patients on maintenance hemodialysis were tested for alanine aminotransferase (ALT), hepatitis B surface antigen (HBsAg), second-generation HCV antibody (anti-HCV), anti-envelope protein 2 antibody (anti-E2) and RNA of GBV-C/HGV, HCV RNA and TTV DNA. Sera of patients with positive TTV DNA, GBV-C/HGV RNA or HCV RNA were tested for viruses 2 years later. Results: Seven (8.2%) 29 (34.1%), 21 (24.7%), 12 (14.1%) and 9 (10.6%) hemodialysis patients were positive for HBsAg, Anti-HCV, HCV RNA, GBV-C/HGV RNA and anti-E2, respectively. TTV DNA was positive in 46 (54.1%) patients. Neither clinical nor virological factors were associated with TTV viremia. The ALT level was significantly elevated in HCV RNA-positive individuals than –negative ones (34.5 vs. 12.5%, p < 0.05). TTV DNA, GBV-C/HGV RNA and HCV RNA remained detectable in sera of 31 (86.1%), 6 (50%) and 21 (100%) patients collected 2 years after first diagnosis of viremia. Conclusion: Among Taiwanese hemodialysis patients, TTV infection is highly prevalent. No clinical or virological factor was observed to be significantly associated with TTV infection. The ALT abnormality was mainly attributable to HCV but not TTV infection in Taiwanese hemodialysis patients.