Epstein-Barr virus (EBV) has been implicated in the pathogenesis of primary central nervous system lymphomas (PCNLs) in immunocompetent hosts. To investigate the role of EBV in the pathogenesis of PCNLs in immunocompetent hosts, this study assessed six PCNL cases (elderly male immunocompetent patients; age ≥60 years) histologically and immunohistochemically, and an EBV genetic study was performed. Histologically, all cases were diagnosed as diffuse large B-cell lymphoma with extensive necrosis. In all six cases, PCNL cells showed immunohistochemical positivity for latent membrane protein 1 (LMP-1) and Epstein-Barr nuclear 2 (EBNA2). Lymphoma cells also showed positive signals for EBV-encoded small RNAs (EBERs) on in-situ hybridization. EBV subtyping-PCR analysis demonstrated that one case was EBNA 2B type and the other five cases were EBNA 2A type, and two cases were EBV wild-type and four cases showed 30-bp LMP-1 deletion by PCR analysis. It is therefore possible that LMP gene deletion or EBNA-2 strain type are important in the tumorigenesis of EBV-positive PCNLs. In addition, EBV-positive PCNLs in immunocompetent hosts may be related to immunological deterioration derived from the aging process.