Purpose In chronic renal failure, intermittent hemodialysis decreases cerebral blood flow velocity (CBFV); however, in critically ill patients with acute renal failure, the effect of continuous venovenous hemodialysis (CVVHD) on CBFV and cerebrovascular autoregulation (AR) is unknown. Therefore, a study was undertaken to investigate the potential effect of CVVHD on CBFV and AR in patients with acute renal failure. Methods This cohort study investigated 20 patients with acute renal failure who required CVVHD. In these patients, the CBFV and index of AR (Mx) were measured using transcranial Doppler before and during CVVHD. Conclusion Compared with patients with intermittent hemodialysis, CVVHD did not influence CBFV and AR in critically ill patients with acute renal failure, possibly due to lower extracorporeal blood flow, slower change of plasma osmolarity, and a lower fluid extraction rate. In a subgroup of patients with sepsis, the AR was impaired at baseline in more than half of the patients, and this was reversed during CVVHD. The trial was registered at ClinicalTrials.gov ID: NCT01376531.Author contributions Patrick Schramm, Christian Werner, and Kristin Engelhard contributed to the conception and design of the study. Patrick Schramm, Dorothea Closhen, Janosch Wojciechowski, Klaus Ulrich Klein, Marc Bodenstein, Christian Werner, and Kristin Engelhard contributed to the acquisition of data. Patrick Schramm, Manfred Berres, Christian Werner, and Kristin Engelhard contributed to the analysis of the data. Patrick Schramm, Christian Werner, and Kristin Engelhard contributed to the interpretation of the data. Patrick Schramm drafted the article. Dorothea Closhen, Janosch Wojciechowski, Klaus Ulrich Klein, Marc Bodenstein, Manfred Berres, Christian Werner, and Kristin Engelhard contributed to revising the article for important intellectual content. Manfred Berres contributed to statistical planning. To avoid adverse effects of cerebral hypo-and hyperperfusion, cerebral blood flow is autoregulated within a wide range of arterial blood pressure changes. This so-called cerebrovascular autoregulation (AR) is impaired in patients with intracranial pathology 1,2 and, likewise, in critically ill septic patients without cerebral pathologies.3 These patients often develop further organ dysfunction, such as acute renal failure with the consequent need for renal replacement therapy. Extracorporeal continuous venovenous hemodialysis (CVVHD) is one kind of renal replacement therapy used in the intensive care unit (ICU) in critically ill patients.