Objective: Pre-existing renal failure serves as a risk factor in the development of acute renal failure. Furthermore, superimposed acute on chronic renal failure is connected with an increased mortality and risk of progression to end stage renal failure. Methods: A new two-stage rat model was developed, where 5/6 nephrectomy was performed, followed by lethal intestinal ischemia and reperfusion. Wistar male rats were used, all initially undergoing either 5/6 nephrectomy or sham operation. Two weeks later half of each group were exposed to clamping of the superior mesenteric artery. Rats were placed in metabolic cages and water intake and urine output was determined. Results: During the two weeks of induction of renal failure, the nephrectomised rats develop polyuria and polydipsia (urine output: 112.2±8.8 ml/min/kg in nephrectomised vs. 36.5±2.3 ml/min/kg in sham operated, p < 0.05 and water intake: 144.1±6.3 ml/min/kg in nephrectomised vs. 61.9±3.1 ml/min/kg in sham operated, p < 0.05). The 5/6 nephrectomised rats had an earlier mortality during development of acute renal failure compared to sham operated rats (71±7 min vs. 122±11 min of reperfusion). Mean arterial pressure were higher during development of multiple organ failure in sham operated compared to nephrectomised rats, although not significantly at all time points. Conclusion: These results suggest that even mild pre-existing renal failure has a critical impact on survival during development of acute renal failure.