BACKGROUND The acute kidney injury (AKI) is a complex disease for which there is no accepted standard definition nowadays. The Acute Kidney Injury Network (AKIN) represents an attempt to standardize the criteria for diagnosis and staging of acute renal dysfunction based on recently published RIFLE criteria, that means, (Risk, Injury, Failure, Loss, and End-stage kidney disease). OBJECTIVE To evaluate the incidence and associated mortality of AKI in patients submitted to on-pump coronary artery bypass graft surgery (on-pump CABG). METHODS A total of 817 patients were divided into two groups: negative AKI (-), with 421 patients (51.5%), and positive AKI (+), with 396 patients (48.5%). Increase of 0.3 mg/dL in creatinine or of 50% in creatinine's basal value was considered as AKI. RESULTS The rate of patient's mortality with or without AKI within 30 days after cardiac surgery was 12.6% and 1.4%, respectively (p<0.0001). In a multivariate logistic regression model, AKI after on-pump CABG was an independent predictor of death within 30 days (OR=6.7; p=0.0002). This group of patients presented a longer period of permanency in intensive care unit (ICU) [median 2 days (2 to 3) versus 3 days (2 to 5); p=0.0001] and a bigger proportion of patients with prolonged permanence in intensive care (>14 days) (14 versus 2%; p=0.0001). CONCLUSIONS In the studied population, even a discrete alteration in renal function, based on AKIN criteria, was an independent predictor of death in 30 days after on-pump CABG.