The majority of cases of acute renal failure (ARF)occur in hospital, most commonly due to acute tubule necrosis caused by multiple nephrotoxic insults, particularly hypovolaemia, hypotension and nephrotoxic drugs. In- hospital ARF carries a high mortality rate, and every attempt should be made to identify at-risk patients and prevent its development by suitable hydration and avoidance of nephrotoxins. Out-of-hospital ARF typically presents as single organ disease, and, if the cause is readily identified and treated, often carries a good prognosis. ARF diagnoses that require specific treatment, particularly urinary tract obstruction and rapidly progressive glomerulonephritis,must not be missed. The immediate priority for all patients with ARF is to make them safe from potentially life-threatening metabolic sequelae, with early referral to a nephrologist in case acute dialysis becomes necessary.