Background:In the critically ill, ischemia secondary to decreased renal blood flow (RBF) is believed to be central to the pathogenesis of acute renal failure (ARF); however, the scientific basis for this conclusion has not been systematically evaluated. Methods: Systematic interrogation of the Pubmed database, and screening bibliographies of retrieved reports, for studies of human ARF where RBF was measured. Results: Thirty-two articles published between 1944 and 2008 describing RBF in 373 patients with ARF were identified. Overall, mean RBF during ARF was 387 ml/min. It was 329 ml/min when estimated by clearance-based techniques (15 studies) and 471 ml/min when measured with nonclearance-based techniques (17 studies). Only 46 patients had measurements in the intensive care unit where mean RBF was 306 ml/min. Normal RBF was reported in 14 publications, mean 1,192 ml/min. Conclusions: Limited information is available on RBF during ARF in the critically ill. Measurements in contemporary patients are required to further our understanding of this condition.