OBJECTIVES: Acute kidney injury (AKI) is a serious complication of cardiac surgery and is consistently associated with poor outcomes.  Nevertheless, due to differences in surgical procedures and approaches to identifying AKI, the costs and outcomes vary across studies. This study aimed to determine the length of stay, costs, and mortality attributable to AKI in high risk cardiac surgery (HRCS) patients from a large database over 10 years. METHODS: Using the comprehensive administrative hospital database from Premier, which includes 20% of all hospitalizations in the US, adults undergoing coronary artery bypass grafting (CABG), cardiac valve replacement or aortic repair surgery between 2000-2011 were identified.  AKI was identified perioperatively from ICD-9 diagnosis codes.  Cost and LOS were also determined using claim and discharge data.  Patients having a post-operative AKI event coded were compared to matched controls based upon age, HRCS type, surgery year, provider facility, and admission type. RESULTS: Of the 142,550 HRCS admissions meeting our criteria, 25,849 (18.1%) had AKI.  Matching was successful in 83.2% of the cases, leading to 21,514 cases and 21,514 controls. Sixty-six percent of the cases were classified as high risk CABG, 7.9% as valve replacement and 26.0% as aortic repair surgery.  Of the cases, 19.6% vs. 3.3% of the controls (p<.001) died during hospitalization. The mean overall cost of post-operative care for patients with AKI was $67,089 (95% CI: 66,166 - 68,012) versus $39,657 (95% CI: 39,274 - 40,040) for controls (p<0.001).  Median cost for cases was $49,372 versus $34,277 for controls (p<0.001). Mean length of ICU/total postoperative lengths of stay for admissions were 5.76/16.83 days for patients with AKI compared with 2.14/ 8.67 days for controls (p<0.001/p<0.001).  CONCLUSIONS: AKI is associated with significantly increases in mortality, LOS, and costs across the post-operative HRCS patients.