An arteriovenous fistula is an abnormal connection between the arterial and venous systems. In the literature, there are well-described ultrasound findings of iatrogenic arteriovenous fistula as a potential complication from percutaneous transarterial or transvenous procedures. The most important sign is direct visualization of the fistula in the place of the access site. It is necessary to look for secondary signs of arterialization of the veins, which can suggest a diagnosis of an arteriovenous fistula. However, the accuracy and diagnostic quality of duplex scanning in the diagnostics of a congenital or spontaneous arteriovenous fistula of the head and neck area in adults have been poorly described in the literature. In this study, we discuss the opportunities of duplex scanning, based on two different cases of an arteriovenous fistula revealed by ultrasound and then confirmed by computer tomographic angiography.