TT virus (TTV) was recently identified as a candidate for a new hepatitis virus. In the present study, the clinical features and transmission routes of TTV infection were analyzed in an area highly endemic for hepatitis C virus (HCV) infection, and compared to those in an area not endemic. In conclusion, the prevalence of TTV infection was as high as 58% in the high-endemicity area for HCV infection. The main transmission route for TTV appeared to be different from that of HCV and HGV. TTV infection showed a reciprocal association with HCV infection, and had limited pathogenetic effect on hepatitis.