We describe unusually marked hyperuricemia and tumor lysis syndrome in a patient with Burkitt type leukemia. A 62-year-old Japanese man was introduced to our hospital because of an emergence of blastic cells in peripheral blood and acute renal failure. On admission, his vital signs were almost normal, but with oliguria. The levels of serum uric acid, creatinine, and urea nitrogen were 43.3 mg/dl, 7.4 mg/dl, and 83 mg/dl, respectively, indicating marked hyperuricemia that we had never seen before and acute renal failure. An increased phosphorous level indicated tumor lysis syndrome. The bone marrow examination confirmed his diagnosis as acute lymphoblastic leukemia (L3 by FAB classification, Burkitt type). The patient was initially treated using continuous hemodiafiltration (CHDF) to support renal dysfunction and to decrease a serum uric acid level. Chemotherapy was initiated using the combination of cyclophosphamide, doxorubixin, vincristine, and dexamehtazone (Hyper-CVAD) on the 5th day from the start of CHDF when his serum uric acid and creati.nine were 10.7 mg/dl and 1.78 mg/dl, respectively. On the 28th day from the start of the chemotherapy, the disease achieved complete remission with a normalized uric acid level (2.6 mg/dl) and recovered renal function. Hyperuricemia of this patient was due to decreased renal excretion of uric acid, although cancer-associated hyperuricemia is usually attributed to the overproduction of uric acid. Burkitt type leukemia/lymphoma causes hyperuricemia and TLS frequently. This patient’s uric acid level was unusu.ally high according to the literature search. Nevertheless, he was successfully treated using CHDF and safely underwent the chemotherapy.