Because the kidney is one of the most important vital organs, renal dysfunction/failure gives great influence on the operative prognosis. Therefore, it is necessary to evaluate the renal function preoperatively. There are many laboratory tests to evaluate kidney function, and serum creatinine level and creatinine clearance are the most valuable parameters of glomerular function. Renal dysfunction is an important independent predictor of in-hospital and late mortality in adult patients undergoing cardiac surgery. In addition, AKIN classification, which synthesized the serum creatinine and urine output, will be useful for prediction of the operative mortality.