Objectives: Consensus definitions represent an important step toward defining the epidemiology of acute kidney injury (AKI). However, the oliguric component of these definitions remains of uncertain impact and utility after cardiac surgery. The authors sought to define the specific impact of oliguric criteria, both alone and in combination with serum creatinine criteria, on the observed incidence of AKI and associated adverse outcomes following adult cardiac surgery. Design: Retrospective observational study over a 1-year period. Setting: Academic medical institution. Participants: A total of 311 adult patients undergoing elective valve and/or coronary artery bypass graft surgery with cardiopulmonary bypass. Interventions: No interventions were performed as part of the study. Measurements and Main Results: Hourly urine output and daily serum creatinine were recorded in the 2 days following surgery. AKI was defined by Acute Kidney Injury Network oliguric and serum creatinine criteria. Defined by serum creatinine criteria alone, the incidence of AKI was 17.7 and was associated strongly with in-hospital mortality (odds ratio 6.6, 95 confidence interval 1.4-30.5, p = 0.02) and renal replacement therapy (odds ratio 12.7, 95 confidence interval 2.4-67.3, p = 0.003) as well as time to discharge from the intensive care unit and hospital. Defined by oliguric criteria alone through 48 hours following surgery, the incidence of AKI dramatically increased to 55.6 but was not associated with mortality, renal replacement therapy, or time to discharge. Conclusions: Acute Kidney Injury Network oliguric criteria applied over 48 hours after surgery dramatically increased the measured incidence of AKI after cardiac surgery, but was not associated with adverse outcomes. ? 2013 Elsevier Inc.