The risk for renal insufficiency by uric acid precipitation in medulla of kidney correlates with the degree of uric acid supersaturation in the urine, depending on uric acid concentration and urinary pH. The patients with gout or hyperuricemia have sometimes acidic urine and increased uric acid excretion. Accordingly, these patients frequently accompany by renal insufficiency. Improvement of hyperuricosuria, increasing of urine volume, and alkalinization of urine to pH6 6.5, are effective for the prevention from renal insufficiency. Acute renal failure related to hyperuricemia, can also occured secondary to cell lysis. Tumor lysis syndrome is a critical illness characterized by massive tumor cell death leading to severe hyperuricemia, hyperphosphatemia, hypocalcemia, and acute renal failure after starting chemotherapy to cancers, especially lymphoproliferative malignancies. Administration of allopurinol 500-600 mg and adequate hydration and alkalinization of urine are advocated to prevent acute renal failure. Intensive care with hemodialysis is often required to treat renal failure, because renal failure is reversible in most cases.