Thirty patients with chronic active Epstein-Barr virus (CAEBV) infection were analyzed. The study group included 18 male and12 female patients, ranging in age from 5 to 31 years with a meanage of 14.2 years. Not all patients had high titers of EBV-specificantibodies, but all patients had high viral loads in their peripheralblood (more than 102.5 copies/µg DNA). Fifty percent of the patients displayed chromosomalaberrations, and 79% had monoclonality of EBV. Patients were dividedinto 2 clinically distinct groups, based on whether the predominantlyinfected cells in their peripheral blood were T cells or naturalkiller (NK) cells. Over a 68-month period of observation, 10 patientsdied from hepatic failure, malignant lymphoma, or other causes.Patients with T-cell CAEBV had a shorter survival time than thosewith NK-cell type ofdisease. (Blood. 2001;98:280-286)