Arteriovenous fistula (AVF) is a rare complication of the abdominal aortic aneurysm (AAA) with complex clinical features. However, AVF and AAA usually cause no symptoms except when they rupture. This case study demonstrated that ultrasonography was a rapid and non-invasive method for the initial assessment of AAA and AVF. A 65-year-old man was admitted to the intensive care unit with hepatic and renal dysfunction. Physical examination revealed an abdominal vascular murmur and bilateral toe discoloration. Ultrasonic examination revealed an AAA and right common iliac artery aneurysm with an AVF located between the right common iliac artery and inferior vena cava. A computed tomography scan confirmed the sonographic findings. We propose that ultrasound should be used more commonly as part of the initial evaluation of the potential and established vascular diseases.