BACKGROUND: Anecdotal data suggest that approximately 20% of patients with a spontaneous extra- and/or intracranial arterial dissection have multiple arterial involvement. Limited data exist regarding the clinical and angiographic characteristics of patients with multiple arterial dissections. We compared the clinical and angiographic features of patients with spontaneous multiple extra- and/or intracranial arterial dissections with those who have a single arterial dissection. METHODS: A retrospective chart review of the consecutive ischemic stroke database over a 7-year period, maintained at 2 institutions, was conducted to identify patients with spontaneous extra- and/or intracranial arterial dissection. The patients' clinical characteristics and angiographic features (including the artery affected, presence of pseudoaneurysm, fibromuscular dysplasia, and degree of stenosis) were analyzed. RESULTS: A total of 76 patients were admitted with spontaneous extra- and/or intracranial arterial dissection; 46 dissections were confirmed with 4-vessel cerebral angiography. Multiple arterial dissections were found in a total of 10 (22%) patients. Involvement of multiple arteries was more prevalent in the young, when compared to a single spontaneous arterial dissection (7 [70%] in patients <45 years of age v 11 [31%]; P = .03). Patients with multiple arterial dissections had a higher proportion of pseudoaneurysms (9 [90%] v 11 [31%]; P = .001), a higher prevalence of underlying fibromuscular dysplasia (3 [30%] v 3 [8%]; P = .11), and were more likely to involve the posterior circulation (P < .0001). CONCLUSIONS: The presence of multiple, simultaneous spontaneous extra- and/or intracranial arterial dissections must be considered when a single spontaneous arterial dissection is identified.