It has been recently demonstrated that the Epstein-Barr virus (EBV) can infect human thymocytes and may be involved in the T cell neoplasms, in addition to African Burkitt's lymphoma, nasopharyngeal carcinoma and Hodgkin's disease. Four distinct clinicopathologic categories of EBV-associated T cell malignancies have been recognized. The angiocentric T cell lymphoma or lymphomatoid granulomatosis involving the nose (or midline lethal granuloma) and skin is frequently EBV-associated. The other 3 groups include angioimmunoblastic lymphadenopathy-like lymphoma, node-based T immunoblastic lymphoma which may contain Reed-Sternberg-like giant cells (Hodgkin's-like lymphoma), and T cell lymphoma resembling malignant histiocytosis. Both the CD4 and CD8 T cell subsets, and a hitherto undefined T lineage lacking CD4/CD8 expression have been involved. The common clinical features are prolonged fever, skin lesions, lymphadenopathy, hepatosplenomegaly, and pancytopenia. Serologic assays suggest that a chronic active EBV infection may exist in most of these patients. The EBV genomes appear to proliferate in clonal and episomal form in the neoplastic cells which show expression of latent membrane proteins. Although an indolent local phase may exist, the clinical course is aggressive for most patients with frequent development of drug resistance to conventional chemotherapy. EBV-associated T cell lymphoma constitutes a separate entity of virus-associated human diseases and opens a potential field to investigate the pathogenesis of EBV-associated human malignancies.