In a 12-month prospective study of the initial management of patients with acute renal failure (ARF) in East Kent (population 593 000), we evaluated the initial management of ARF and assessed what proportion of ARF may have been preventable. Patients were seen and assessed on a daily basis, and were followed until discharge from hospital or death; survivors were subsequently followed for 3 years. Overall, 288 patients developed ARF (486 per million population/year). Mean age at presentation was 73 years (range 14-96). Initial assessment was often suboptimal, and key features in investigation and initial management were often lacking. In 108 cases, ARF was iatrogenic and/or potentially preventable (53 preventable, 99 iatrogenic, 44 both). Overall survival was 56% at discharge from hospital, 35% at 1-year follow-up, 31% at 2 years, and 28% at 3 years. In discharged patients, recovery of function was complete in 69%. A significant proportion of ARF is preventable. Clear guidelines, easily accessible at the point of care, could aid the diagnostic evaluation of the patient with ARF and indicate where referral for a specialist opinion is appropriate.