We report a 4-year-old boy who developed tumor lysis syndrome complicated by severe hyperphosphatemia and acute renal failure, following chemotherapy for T-cell acute lymphoblastic leukemia. Despite successful treatment of hyperphosphatemia with hemodialysis, there was an immediate rebound in the high serum phosphorus level. The patient underwent a second treatment with hemodialysis which was then followed by continuous veno-venous hemofiltration (CVVH). CVVH maintained his serum phosphorus at a stable level until his renal function improved. CVVH can be used in conjunction with hemodialysis to successfully treat the hyperphosphatemia associated with tumor lysis syndrome.