Hyperuricemia, due to inborn errors of metabolism, dehydration, or tumor lysis, may cause renal insufficiency. Hyperuricemia from tumor lysis syndrome in malignancy is usually associated with electrolyte disturbances such as hyperkalemia, hyperphosphatemia or hyper or hypocalcemia. Tumor infiltration into the kidneys can occur, yet this accounts for renal insufficiency in only 1% of patients. This infiltration of tumor cells into the kidneys is usually associated with evidence of malignancy elsewhere as identified by physical exam, radiographic studies, and examination of the peripheral smear or bone marrow. We report an unusual presentation of a child with acute lymphocytic leukemia presenting with acute renal failure, nephromegaly and hyperuricemia without electrolyte disturbances or systemic evidence of tumor elsewhere. We stress the importance of kidney biopsy in order to identify the etiology of the renal failure and hyperuricemia.