Emerging evidences indicate that hepatitis B virus (HBV) infection is associated with non-Hodgkin lymphoma (NHL), but the mechanisms of HBV-induction lymphomagenesis remain unclear. In this report, retrospective analysis of the prevalence of hepatitis B surface antigen (HBsAg) among NHL cases demonstrated significantly higher HBsAg carrier rate among B-cell NHL cases than controls (other cancers except primary liver cancer) (adjusted odds ratio, 1.56; 95% confidence interval, 1.13-2.16). Furthermore, cells with an immortalization potential existed in the peripheral blood of 4 patients with chronic HBV infection. Characterization of these cells showed their immunophenotypes similar to that of the majority of HBsAg-positive B-cell NHL patients. Immunoglobulin (Ig) gene rearrangements confirmed the clonal Ig gene rearrangements. Cytogenetic analysis revealed abnormal karyotypes of these cells with an immortalization potential. Compared with cells with an immortalization potential that we previously found in B-cell NHL patients by the same way, these cells showed many similar features. In conclusion, cells with an immortalization potential existed in the part of patients with chronic HBV infection before lymphoma development and showed some malignant features. They may be the cellular basis of HBV-associated lymphomagenesis.