A rare and very aggressive neoplastic disease emerging after a primary acute or chronic active EBV infection. It presents with persisting fever and malaise, hepatosplenomegaly with or without lymphadenopathy, liver failure, severe pancytopenia and a rapid progression towards multi-organ failure and hemophagocytic syndrome with a fatal issue. It is characterized by clonal proliferation of EBV-infected T cells with an activated cytotoxic phenotype.