A 66-year-old woman treated for ocular myasthenia gravis with azathioprine for 12 years presented with a left fronto-parietal mass. Histology revealed primary Hodgkin's lymphoma of the central nervous system with CD30, Epstein-Barr virus (EBV) latent membrane protein and CD20-positive, CD45 (LCA)-negative Reed-Sternberg cells surrounded by T cells. Moreover, EBV-encoded RNA-1 (EBER-1) sequences and a monoclonal rearrangement of the immunoglobulin heavy chain CDR2 locus were detected.