We prospectively evaluated 15 consecutive patients with spontaneous cervical artery dissections. Three patients (20%) had a heritable connective tissue disorder, each with a unique phenotype. None of these patients met the criteria of any of the named syndromes, and collagen and fibrillin analyses were normal. Heritable connective tissue disorders are common among patients with spontaneous cervical artery dissections, but, despite intensive investigations, the type of disorder usually cannot be identified. The underlying arteriopathy in cervical artery dissections is likely to be heterogeneous.