A Japanese male patient received various medications for his long-standing rheumatoid arthritis (stage IV, class II). He developed a mass on the right anterior chest wall after being treated with methotrexate (MTX) for 4 months. A biopsy of the mass showed it to be Epstein Barr virus (EBV)-associated lymphoma of B-cell phenotype stage IE (bulky mass), with positive EBV-encoded small RNAs (EBERs) in situ hybridization, EBV latent membrane protein-1 (LMP-1) negative, EB nuclear antigen-2 (ERNA-2) negative, CD20/L26 (+), CD45RO/UCHL-1 (-). A single band of the joined termini of the EBV genome was demonstrated in DNA extracted from the mass, suggesting a clonal disorder of the mass. Immunostaining of the mass with p53 antibody was also positive. With discontinuation of MTX and administration of chemotherapy, the tumor disappeared but recurred after 3 months. This case suggests that concordant p53 expression and latent EBV infection may play an important role in the pathogenesis of lymphomas arising in patients with rheumatoid arthritis who are immunosuppressed with MTX.