We describe a clinical case presenting two unusual features. The first was a spontaneous aorto-caval fistula which had developed from rupture of an atherosclerotic aortic aneurysm into the inferior vena cava. The second uncommon feature depended on the unusual method by which the diagnosis was performed. In fact, using an echo-Doppler color flow (HP 77020A ultrasound system) with a 2.5 MHz echocardiographic probe abdominal examination revealed an aneurysm of the abdominal aorta that communicated with a dilated inferior vena cava. Furthermore, flow study with pulsed color Doppler revealed a continuous turbolent, mixed (arterial and venous) blood flow into the vena cava.