OBJECTIVES: Widely disparate definitions of renal injury or failure have historically been used in epidemiologic studies, not always in accordance with the RIFLE (risk, injury and failure) criteria. This has resulted in a wide range of incidence rates in the published literature. The clinical epidemiology analysis of AKI estimates an incidence rate of 200/100,000 in the all-age population and 25/100,000 in the all-age population receiving renal replacement therapy. Our objective was to estimate the prevalence and examine the related health care burden of acute kidney injury (AKI).   METHODS: Patients diagnosed with AKI in 2009 were identified in the OptumInsight Impact database.  Projections for the US Population were based on the age-adjusted prevalence per 100,000 for patients with at least one paid claim that specified an AKI diagnosis during 2009.  A sample matched for age and gender was created to compare health care costs. RESULTS: Based on the age-adjusted prevalence in the OptumInsight Impact database of 480 per 100,000 patients in 2009, the projection to the US population was 1,473,232 individuals with AKI; 40% of these patients were exposed to contrast media; nearly 30% had cardiovascular (CV) surgery, and over 20% of patients also had major digestive surgery.   Mean annual costs in 2009 were $64,594, including outpatient, inpatient, ER, and pharmacy (N=116,994 AKI patients).  This included costs specifically related to AKI ($19,115).  Among AKI patients that had dialysis, the mean annual procedure-related costs ($44,065, N=10,879) were comparable to all patients receiving dialysis ($46,884).  However, AKI patients typically demonstrated substantially higher procedure-related costs for major digestive surgery, major CV surgery, and contrast media exposure, in comparison to all patients undergoing each of these procedures. CONCLUSIONS: AKI prevalence was higher than expected, and was associated with a high economic burden as demonstrated by procedure-related costs.  To understand the pattern of risk, longitudinal examination is needed.