This study assessed the association of hepatitis B virus (HBV) and hepatitis C virus (HCV) infection with non-Hodgkin's lymphoma in a highly HBVendemic area. The prevalence of either HBV or HCV infection in 235 patients with non-Hodgkin's lymphoma was compared with that of an age- and sex-matched hospital control group of 235 patients. The prevalence of HBV infection was higher in B-cell non-Hodgkin's lymphoma (15.5%) than control (8.1%), but the prevalence of HCV infection in the non-Hodgkin's lymphoma patients (2.1%) and control group (3%) was similar. HBV prevalence increased significantly with age in the B-cell non-Hodgkin's lymphoma patients. The presence of HBV proteins and DNA in lymphoma tissues and peripheral blood mononuclear cells (PBMCs) from HBV-infected non-Hodgkin's lymphoma patients was also investigated using immunohistochemistry and PCR. HBV DNA was frequently detected in PBMCs from HBV-infected non-Hodgkin's lymphoma patients, but HBV antigens were not. Therefore, HBV infection, but not HCV infection, was associated with B-cell non-Hodgkin's lymphoma in Korea, suggesting a possible role for HBV in the development of non-Hodgkin's lymphoma.