Acute renal failure (ARF) is a syndrome commonly seen in the ICU. It is usually multifactorial rather than the result of a primary renal disease. The difficulty of adequately defining the syndrome has been addressed by the Acute Dialysis Quality Initiative, leading to the RIFLE criteria. The model of prerenal, intrinsic, and postrenal failure is still helpful for diagnosis and instigating appropriate investigation and therapy. The focus should be on vigilance to prevent prerenal failure progressing to established renal failure. Therefore, management should correct for any ciculatory and respiratory impairment, exclude any urinary tract obstruction, avoid toxic medications, establish the cause of ARF and treat life-threatening complications, such as hyperkalaemia and acidaemia. The indications and methods of administering renal replacement therapy are discussed in this article. Evidence supporting one form of renal replacement over another is unclear, although it appears both the dose and early initiation of renal replacement can influence outcome. Of those patients requiring renal replacement therapy who survive ICU admission, few require long-term dialysis, particularly if no premorbid renal dysfunction existed. © 2006 Elsevier Ltd. All rights reserved.