Intracranial aneurysms, arteriovenous malformations (AVMs), and cerebral cavernous malformation (CCMs) are relatively common cerebrovascular lesions that can result severe neurological morbidity and mortality in a significant number of individuals who harbor them. These lesions most often occur sporadically. However, familial forms have been identified in a subset of cases. Considerable progress has been made over the past decade in the molecular genetics of these lesions. The identification of gene mutations and other genetic risk factors have improved the clinical management of patients and their relatives are discussed in this chapter.