Background/Aims: Cardiac surgery-associated severe acute kidney injury (SAKI) is associated with high mortality and poor quality of life. A prognostic score for SAKI may enable prevention of complications. Methods: This observational study of 2,552 patients undergoing cardiac surgery from January 2006 to December 2011 in our institution established associations between predictor variables and postoperative SAKI from a cohort of 1,692 patients and developed a clinical score that was assessed in a validation cohort of 860 patients. Results: Postoperative SAKI occurred in 262 patients (10.3%). We identified 7 independent and significant risk factors in the derivation model (adjusted OR 95%CI): age >= 81 years (vs. age < 40 years, 4.30, 1.52-12.21), age 61-80 years (vs. age <40years, 2.84, 1.24-6.52), age 41-60 years (vs. age < 40 years, 1.62, 0.68-3.87), hypertension (1.65, 1.13-2.39), previous cardiac surgery (3.62, 1.27-10.32), hyperuricemia (2.02, 1.40-2.92), prolonged operation time (1.32, 1.17-1.48), postoperative central venous pressure < 6mmH₂O (3.53, 2.38-5.23), and low postoperative cardiac output (4.78, 2.97-7.69). The 7-variable risk prediction model had acceptable performance characteristics in the validation cohort (C statistic 0.80, 95% CI 0.74-0.85). The difference in the C statistic was 0.21 (95% CI 0.12-0.29, p < 0.001) compared with the Cleveland Clinic score. Conclusion: We developed and validated a practical risk prediction model for SAKI after cardiac surgery based on routinely available perioperative clinical and laboratory data. The prediction model can be easily applied at the bedside and provides a simple and interpretable estimation of risk.