To review recent studies and information on the relationship between fluid administration and kidney function in critically ill patients. Recent findings There is little evidence from large multicenter trials to direct fluid therapy in patients at risk of acute kidney injury (AKI). Evidence of benefit for fluid administration from single center studies of fluid resuscitation to hemodynamic goals needs to be weighed against evidence of harm associated with fluid overload in large observational studies. The composition of intravenous fluid may affect the risk of AKI. Even latest-generation hydroxyethyl starches increase the risk of severe AKI in general and septic ICU patients. Isotonic saline has been associated with greater incidence of AKI in comparison to buffered crystalloids. Experimentally, infusion of saline results in reduction in renal perfusion in comparison to buffered solutions. Summary Clinicians need to weigh the balance between adequate resuscitation of cardiac output and avoidance of fluid overload. Protocolized resuscitation to hemodynamic goals may help achieve these conflicting goals at least in the early phases of critical illness. In critically ill patients with, or at risk of, AKI, clinicians should avoid starch and, possibly, saline solutions.