Background: Acute kidney injury (AKI) is common in patients with acute myocardial infarction (AMI) and is associated with permanent renal impairment and death. Although guidelines increasingly emphasize AKI prevention, whether increased awareness has translated into reduced AKI rates is unclear. Methods: Among 33 249 consecutive hospitalizations in 31 532 unselected patients with AMI across 56 US centers from Cerner Corporation's HealthFacts database, we examined the temporal trends in AKI incidence from 2000 to 2008. Acute kidney injury was defined as an absolute increase in creatinine level of at least 0.3 mg/dL or a relative increase of at least 50% during hospitalization. Results: From 2000 to 2008, the mean age of patients increased (from 66.5 to 68.6 years), as did the known AKI risk factors, including chronic kidney disease, cardiogenic shock, diabetes mellitus, heart failure, coronary angiography, and percutaneous coronary intervention. Despite this, AKI incidence declined from 26.6% in 2000 to 19.7% in 2008 (P<.001). After multivariate adjustment, the trend of decreasing AKI rates persisted (4.4% decline per year; P<.001). In addition, inhospital mortality also declined over time among patients developing AKI, from 19.9% in 2000 to 13.8% in 2008 (P=.003). Conclusions: In a large national study, AKI incidence in patients hospitalized with AMI declined significantly from 2000 to 2008 despite the aging population and rising prevalence of AKI risk factors. These findings may reflect increased clinician awareness, better risk stratification, or greater use of AKI prevention efforts during this time period.