Fibromuscular dysplasia is an idiopathic vascular disease with fibromuscular thickening of the arterial wall. The intima, media, or adventitia can be involved, with medial involvement by far the most common. By location, the most common areas involved are the renal and cervical (carotid or vertebral) arteries.

The classic appearance is the "string of beads" where there are alternating concentric stenosis and dilatations as seen in involvement of the media.

Other, rarer manifestations are also possible including vascular loops, aneurysms, or fusiform ectasia.