Cerebral cavernous malformations (CCM) are vascular lesions which can occur as a sporadic (80% of the cases) or familial autosomal dominant form (20%). Three CCM genes have been identified: CCM1/KRIT1, CCM2/MGC4607 and CCM3/PDCD10. Almost 80% of CCM patients affected with a genetic form of the disease harbor a heterozygous germline mutation in one of these three genes. Recent work has shown that a two-hit mechanism is involved in CCM pathogenesis which is caused by a complete loss of any of the three CCM proteins within endothelial cells lining the cavernous capillary cavities. These data were an important step towards the elucidation of the mechanisms of this condition.