In addition to clinical signs and symptoms, laboratory and radiologic studies, diagnosis of vascular disorders has historically relied on gross and histopathologic evaluation of affected vessels. This chapter will explore the pathologic conditions that can affect the extracranial carotid and vertebral arteries (ECCAs and ECVAs)with emphasis on their characteristic histopathologic features and pathogenesis. Pathologic conditions affecting these vessels are clinically important because they can lead to severe cerebrovascular complications, including transient ischemic attack (TIA) and stroke, and are often managed by surgical techniques. The diseases covered include atherosclerosis, dissection, aneurysm, fibromuscular dysplasia, and vasculitis. The pathologic features of the carotid body tumor (or paraganglioma) will also be discussed.