The incidence of aorto-enteric fistula in the first 5 years after abdominal aortic replacement ranges from 0.3 to 2%. We present a clinical case in which all conventional diagnostic tools failed to demonstrate the aorto-enteric fistula. A 73 year-old male suffering intermittent episodes of melena without signs and symptoms of infection was repeatedly admitted at our institution. All conventional diagnostic tools failed to show the bleeding source. Precise diagnosis was obtained using intra vascular ultrasound (IVUS). IVUS allowed prompt diagnosis of the aorto-duodenal fistula and opened the way to its endovascular treatment.