Lymphomatoid granulomatosis (LG) exhibits many similarities both clinically and pathologically to angiocentric T/NK cell lymphoma and was until recently considered to be part of the same disease spectrum. However, recent data indicate that LG is an EBV positive B cell proliferation associated with an exuberant T cell reaction. LG presents in extranodal sites, most commonly the lung (Katzenstein and Peiper, 1990). Other frequent sites of involvement include kidney, skin, central nervous system and liver. The pattern of necrosis in both LG and T/NK cell lymphoma is very similar, emphasizing the probable importance of EBV in mediating the vascular damage. Recent studies implicate the chemokines IP-10 and Mig in the pathogenesis of the vascular damage. Although the predominant infiltrating cells are T cells, the T cell receptor genes are not clonally rearranged. However, by VDJ polymerase chain reaction, approximately 60% of cases contain clonal rearrangements. EBV sequences can be localized to B cells and are clonal in most cases. Most patients with LG when carefully evaluated clinically have defects in cytotoxic T cell function and reduced levels of CD8+ T cells. LG is also common in many immunodeficiency states, such as AIDS, Wiskott-Aldrich syndrome and post-transplantation immunodeficiency. Thus, in many respects, LG resembles an EBV driven lymphoproliferative disorder. Some cases of LG regress spontaneously, but most patients require therapy. Treatment approaches have included cyclophosphamide and prednisone, aggressive combination chemotherapy and interferon alpha 2b, because of its antiviral, antiproliferative and immunomodulatory effects.