Aortocaval fistula (ACF) in patients operated for Ruptured Acute Aorta Aneurysm (rAAA): A surgical challenge. Introduction Aortocaval fistula is a rare complication of abdominal aortic aneurysm (AAA). It been reported to be present in less than 1% of all AAAs. ACF arise in patients with large aneurysms and is typically discovered peroperatively in patients with rAAA. Open surgical treatment is associated with high mortality and morbidity. ACF is a result of spontaneously rupture of large atherosclerotic aneurysms into the inferior vena cava in 80%, 15% arise after trauma and 5% are iatrogenic. Patients During the last 9 month, we have operated three cases with rAAA and ACF. All patients had an open, acute operation. All ACFs detected during operation. Common for all operations was that the patients had large aneurysms (>10 cm) and extensive bleeding (3-4 l) immediately when the aneurysm was clamped and opened. CT examinations done before operation but ACF not detected before the operation. All patients survived but the recovery marked by morbidity in different ways. Results Reviewing the literature, most papers include single cases and a few systemic reviews on endovascular treatment of ACF. We have reviewed ACF in a perspective of history, pathophysiology, symptomatology, and consideration of examinations, treatment now and in the future. Conclusion ACF is difficult to detect on a preoperative CT-scan. Hence, the true incidence may be underestimated. Vascular surgeon needs to know the condition and to be aware of it, since it is important to have a strategy for treatment during operation for rAAA. A screening program for AAA in the future may detect and avoid ACF in patients with large aneurysms. New endovascular treatment may decrease morbidity and mortality.