To evaluate whether HCV genotype and a "silent" HBV infection may be related to a more severe clinical presentation of liver disease, 205 anti-HCV/HCV-RNA positive, HBsAg/anti-HBs negative patients with chronic hepatitis (113 males and 92 females; median age 55 years, range 18-77), were studied on presentation at the Liver Unit from January 1993 to December 1997. Presence of serum anti-HBc, in the absence of HBsAg and anti-HBs, was considered a marker of "silent" HBV infection. Of the 205 patients, 134 had undergone percutaneous liver biopsy. Two main diagnosis groups were established: the mild liver disease group (76 patients), and the severe liver disease group (109 patients); 20 patients who had refused to undergo liver biopsy were not included in the clinical and virological evaluation because the diagnosis was uncertain. The prevalence of severe liver disease was similar in the genotype 1 and non-1 groups (61.3% of 98 patients with genotype 1 and 52.9% of 70 patients with a non-1 genotype). Instead, the 88 patients with "silent" HBV infection showed a higher percentage of severe liver disease than the 97 anti-HBc negative patients (72.7% vs. 46.4%, respectively: P < 0.0005). Of the 88 anti-HBc positive patients, the prevalence of those with severe liver disease was similar in the 32 cases with serum HBV-DNA as detected by PCR and in the 56 HBV-DNA negative (81.2% vs. 67.8%, P = 0.4). The relation between "silent" HBV infection and severe liver disease was observed both in genotype 1 and non-1 infected patients. Nevertheless, the anti-HBc negative patients infected by genotype 1 showed a severe liver disease more frequently than those infected by a non-1 genotype, with a difference that is significant to the statistical analysis (P < 0.05). The findings suggest that "silent" HBV infection in anti-HCV positive chronic hepatitis enhances the severity of the liver disease. Evidence was also found that in patients without "silent" HBV infection there is a correlation between the presence of HCV genotype 1 and the severity of liver disease.