Fibromuscular dysplasia (FMD) is a rare medical condition. Patients with FMD have abnormal cellular growth in the walls of their medium and large arteries. This can cause the arteries with the abnormal growth to look beaded. The arteries may also become narrow (stenosis). FMD is a predisposing factor in 15% of spontaneous cervical carotid dissections. Dissections in FMD are more commonly multiple than in patients without an identified underlying arteriopathy. FMD lesions likely predispose the artery to dissection through weakening of the arterial wall. Although the multiple manifestations of a structural arteriopathy in FMD hint of a genetic cause, such as collagen or elastin mutation, epidemiologic data suggesting familial transmission are generally weak.