Intracranial dissections have only been reported in small case series. More is known about the pathology, clinical findings, treatment and prognosis related to extracranial dissections. Knowing where within the arterial wall the dissection occurs is important in determining the appropriate treatment and prognosis. If the internal aspect of the artery is dissected, between the intima and media, vascular occlusion with resulting ischemia results. When the dissection plane is between the media and adventitia, bulging of the artery, with resultant aneurysmal dilatation, and vascular rupture can occur. In this chapter on intracranial dissections we will first review the pathology and etiology underlying intracranial dissections, then discuss the clinical aspects of both ischemic and aneurysmal intracranial dissections.