Hepatitis B virus (HBV) infection was evaluated in serum and liver specimens of eight Italian children with primary liver cancer. All children were negative for HBV markers in serum but four of them showed HBV-DNA sequences and/or HBs antigen expression in the liver. In one case, viral DNA was present in both neoplastic and non-neoplastic tissue, while in one case HBV-DNA was detectable only in nontumoral tissue and in one case only in the tumor area. In these cases, scattered HBsAg was expressed in the cytoplasm of cells in normal part of the liver and in another case neoplastic cells secreted HBsAg in culture. In two cases, the histologic diagnosis was HCC; one case had mixed HPB and one had macrotrabecular HPB. All children were more than 1 year of age. The remaining four children were histologically diagnosed as HPB and were less than 1 year of age. These findings suggest that HBV may be a cofactor for the development of liver cancer also in children of Western countries and that the risk of infection progressively increases with age.