The Epstein-Barr virus (EBV) genome exists in tumour cells of T-cell lymphomas in non-immunosuppressed patients. We identified EBV-DNA by in situ hybridization in a case of anaplastic T-cell lymphoma associated with acquired immunodeficiency syndrome (AIDS). EBV-DNA has been reported in AIDS-related Hodgkin's disease or B-cell lymphoma, but never in T-cell lymphoma. Although our results suggest that EBV could play a role in the development of these anaplastic T-cell lymphomas, the mechanism of EBV penetration into T-cells remains uncertain.