Background: The role of GB virus-C/hepatitis G virus (GBV-C/HGV) in fulminant hepatitis (FH) and subfulminant hepatitis (SFH) remains unclear. Methods: Thirty-two FH or SFH patients, with adequate clinical information and serum specimens, were studied. Serum samples were tested for hepatitis markers and genomes of hepatitis A-E viruses, as well as GBV-C/HGV. Results: Of the cases of FH/SFH studied, one (3%) was caused by anti-tuberculosis agents, 26 (81%) had hepatotropic virus infection, and five (16%) had no identifiable cause. Of the 26 patients with hepatotropic virus infection, five had acute hepatitis B infection (one with acute hepatitis D virus (HDV) co-infection), one had acute hepatitis C infection, 16 were hepatitis B surface antigen carriers with reactivation or superimposed by unidentified agent(s) (two had triple virus infections), three were hepatitis B carriers with HDV superinfection, and one had GBV-C/HGV infection in addition to exposure to halothane. GBV-C/HGV-RNA was detected in only three of 32 patients (9%) and all had a history of blood transfusion or co-existing causative factors. Of the 26 patients with hepatotropic virus infection, 18 were tested for antibodies against GBV-C/HGV envelope protein and seven were reactive, suggesting past infection. Conclusions: The role of GBV-C/HGV in causing FH and SFH is minimal in Taiwan and I-IBV infection remains the major aetiology. These findings also suggest the existence of as yet unrecognized agents, responsible for such catastrophic illnesses.