This study focused on 32 patients who were diagnosed as having autoimmune hepatitis based upon clinical and histological factors. Fifteen of these patients were positive for HCV-RNA and for one of the HCV-related markers tested, including anti-C100, ELISA II, and RIBA 2 (Group 2). The remaining 17 patients were negative for all HCV-related markers (Group 1). Clinical factors in the two groups, including the frequency of autoantibodies, serum levels of aminotransferase and gammaglobulin, HLA phenotypes, and the response to corticosteroid treatments, were compared. The titer of serum anti-nuclear antibodies and the level of serum aminotransferase at initial diagnosis were significantly higher in Group 1 than in Group 2. Furthermore, the genetic background of the two groups, as indicated by HLA phenotypes, differed. All cases in Group 1 were HLA-DR4-positive, whereas only 60% of those in Group 2 cases had HLA-DR4. Also, all cases in Group 1 but only 66.7% of the cases in Group 2 showed good clinical responses to corticosteroid treatment. Finally, no cases of HCV-related-marker-positive autoimmune hepatitis (Group 2) had antibodies for LKM, suggesting that these cases were clinically different from type II autoimmune hepatitis. These data indicated that immunosuppressive treatment might be the preferred initial treatment in patients who either satisfy the criteria for AIH or who are sero-positive for an HCV-marker.