A 20-month-old girl had a disorder that by both clinical and histologic criteria resembled the virus-associated hemophagocytic syndrome in the setting of Epstein-Barr virus infection. Subsequent investigation revealed histologic evidence of disseminated T-cell lymphoma. DNA hybridization studies displayed a monoclonal T-cell receptor beta chain rearrangement, in the absence of clonal immunoglobulin gene rearrangement, and a single band in the analysis for the fused termini of the Epstein-Barr virus genome. These results suggest the presence of a monoclonal population of T lymphocytes infected with Epstein-Barr virus. The diagnosis of lymphoma was confirmed at autopsy. The authors discuss the association of Epstein-Barr virus infection with the development of T-cell lymphoma and propose that the previous reports of virus-associated hemophagocytic syndrome include cases of unrecognized T-cell lymphoma.