I.D.E.A.L.-I.C.U. (Initiation of Dialysis EArly Versus deLayed in Intensive Care Unit)

Inclusion Criteria: Adults (males or females, age \>18 years) with septic shock who develop acute renal failure (as defined by the "Failure" stage of the RIFLE classification) will be eligible for inclusion. Septic shock is defined as severe sepsis with at least 2 to 4 "SIRS" criteria and persistent hypotension despite adequate vascular filling and need vaso-active drugs. SIRS is defined as the simultaneous presence of at least 2 of the following criteria : * Body temperature ≥ 38°C ou ≤ 36°C * Heart rate ≥ 90 bpm * Respiratory rate ≥ 20/mn or PaCO2 ≤ 32 mmHg * Leucocytes ≥ 12,000/mm3 or ≤ 4,000/mm3 or \>10% immature forms. Acute renal insufficiency is defined as the "failure" stage of the RIFLE classification, i.e. the presence of at least one of the following criteria: * Increased creatinine x 3 times the baseline value * Oliguria \< 0.3 ml/kg/h for 12 hours * Anuria (diuresis \< 100ml) for at least 12 hours All patients are required to provide informed consent after having been appropriately informed about the study. In case of temporary incapacity of the patient to sign, the consent form can be signed by a surrogate. Exclusion Criteria: Patients presenting any of the following criteria will not be eligible for inclusion in the study: 1. Patients with chronic renal at dialysis. 2. Patients presenting acute renal failure of type obstructive and patients already presenting emergency criteria for immediate hemodialysis at the time of randomization (i.e. hyperkalemia \>6.5 mmol/L or pH\<7.15 or pulmonary oedema by fluid overload) 3. Patients already had hemodialysis before their arrival in the intensive care unit 4. Pregnant women. 5. Moribund patients whose life expectancy is less than 24 hours 6. Patients unlikely to survive to 28 days because of uncontrollable comorbidities (e.g. cardiac, pulmonary or hepatic disease at the terminal stage, hepatorenal syndrome, uncontrolled cancer, severe post-anorexic encephalopathy…) 7. Patients with advance directives indicating their wish not to be resuscitated. 8. Patients under legal guardianship. 9. Patients participing in another interventional study that may influence the prognosis of patients.