Background Acute kidney injury (AKI) has been recognized as a major healthcare problem affecting millions of patients worldwide.However,epidemiologic data concing AKI in China are still lacking.The objectives of this study were to characterize AKI defined by RIFLE criteria,assess the association with hospital mortality,and evaluate the impact of AKI in the context of other risk factors.Methods This prospective multicenter observational study enrolled 3,063 consecutive patients from 1 July 2009 to 31 August 2009 in 22 ICUs across mainland China.We excluded patients who were admitted for less than 24 hours (n=1623),younger than 18 years (n=127),receiving chronic hemodialysis (n=29),receiving renal transplantation (n=1) and unknown reasons (n=28).There were 1255 patients in the final analysis.AKI was diagnosed and classified according to RIFLE criteria.Results There were 396 patients (31.6％) who had AKI,with RIFLE maximum class R,I,and F in 126 (10.0％),91 (7.3％),and 179 (14.3％) patients,respectively.Renal function deteriorated in 206 patients (16.4％).In comparison with non AKI patients,patients in the risk class on ICU admission were more likely to progress to the injury class (odds ratio (OR) 3.564,95％ confidence interval (CI) 1.706-7.443,P =0.001],while patients in the risk class (OR 5.215,95％ CI 2.798-9.719,P ＜0.001) and injury class (OR 13.316,95％ CI 7.507-23.622,P ＜0.001) had a significantly higher probability of deteriorating into failure class.The adjusted hazard ratios for 90-day mortality were 1.884 for the risk group,3.401 for the injury group,and 5.306 for the failure group.Conclusions The prevalence of AKI was high among critically ill patients in Chinese ICUs.In comparison with non-AKI patients,patients with RIFLE class R or class I on ICU admission were more susceptibility to progression to class I or class F.The RIFLE criteria were robust and correlated well with clinical deterioration and mortality.