Adult T-cell leukemia (ATL) is accompanied by remarkably impaired cellular immune responses. Reports on the simultaneous development of ATL and Epstein-Barr virus-associated lymphoproliferative disorders (EBV-LPD) are, however, quite rare. A 53-years-old man was admitted to our hospital because of multiple bilateral pulmonary nodules, skin rash, lymphadenopathy, and hypercalcemia. The smear preparation of peripheral blood demonstrated pathological lymphocytes with lobulated nuclei. They expressed CD2, CD3, and CD25, but did not express either CD4 or CD8. In addition, he was positive for Human T-cell leukemic virus type-I (HTLV-I), and monoclonal integration of HTLV-I provirus was detected in peripheral blood. Unexpectedly, inguinal lymph node biopsy showed polyclonal proliferation of EBV-positive large and bizarre-shaped B cells, and monoclonal growth of large abnormal T cells. He was diagnosed as having acute type ATL complicated by EBV-LPD. Chemotherapy for ATL effectively decreased the tumor burden of ATL, but persistent high fever developed suddenly on the 68th day after admission, and he died of multi-organ failure with severe metabolic acidosis. At the time of multi-organ failure, viral load had increased strikingly, suggesting that the progression of EBV-LPD might have been responsible for multi-organ failure in this case.