The presence of hepatitis B virus (HBV) has been evaluated in liver specimens from 11 children with primary liver tumors and negative results of serologic testing for HBV markers. HBV-DNA sequences were detected by the polymerase chain reaction procedure, using different sets of oligonucleotide primers from highly conserved regions of HBV genome. Two of three children with histologic diagnosis of hepatocellular carcinoma were positive for HBV-DNA in the liver, whereas the remaining children, including six patients with hepatoblastoma, one patient with hemangioma, and one patient with hamartoma, were negative. These findings support the hypothesis of a primary role of HBV in the development of hepatocellular carcinoma in children from nonendemic areas and without overt HBV infection.