The cause of spontaneous cervicocerebral artery dissection is unknown. An underlying arteriopathy due to a connective tissue disorder has often been presumed. We studied 25 patients with proven nontraumatic dissections. The ultrastructural morphology of dermal connective tissue components was assessed by transmission electron microscopy of skin biopsies. Ultrastructural abnormalities were seen in 17 (68%) patients, resembling in some cases the aberrations found in Ehlers-Danlos syndrome type II or III. These observations indicate a correlation of cervical artery dissections with connective tissue abnormalities. A structural abnormality in the extracellular matrix potentially caused by basic molecular defects is suggested and warrants further exploration.