Acute renal failure is present in 1 to 5 percent of patients at hospital admission and affects up to 20 percent of patients in intensive care units. The condition has prerenal, intrarenal, and postrenal causes, with prerenal conditions accounting for 60 to 70 percent of cases. The cause of acute renal failure usually can be identified through an appropriate history, a physical examination, and selected laboratory tests. The initial laboratory evaluation should include urinalysis, a determination of the fractional excretion of sodium, a blood urea nitrogen to creatinine ratio, and a basic metabolic panel. Management includes correction of fluid and electrolyte levels; avoidance of nephrotoxins; and kidney replacement therapy, when appropriate. Several recent studies support the use of acetylcysteine for the prevention of acute renal failure in patients undergoing various procedures. The relative risk of serum creatinine elevation was 0.11 in patients undergoing radiocontrast-media procedures (absolute risk reduction: 19 percent) and 0.33 in patients undergoing coronary angiography (absolute risk reduction: 8 percent). In patients pretreated with sodium bicarbonate before radiocontrast-media procedures, the relative risk of serum creatinine elevation was 0.13 and the absolute risk reduction was 11.9 percent. Dopamine and diuretics have been shown to be ineffective in ameliorating the course of acute renal failure.