Cerebral cavernomas (CCMs) are vascular malformations that may be inherited as an autosomal dominant condition for which a gene, CCM1, was mapped to chromosome 7. Poorly defined cutaneous malformations were sometimes described in association with CCMs. During a national survey, 57 French CCM families were studied. Co-occurrence of CCMs and a distinctive cutaneous vascular malformation was observed in 4 families. Ten individuals belonging to these families showed similar hyperkeratotic cutaneous capillary venous malformations (HCCVMs). In 3 families, the histology showed orthokeratosis and hyperkeratosis as well as dilated capillaries in the dermis extending to the hypodermis and confirmed the diagnosis of HCCVM. Genetic analysis strongly supports linkage of these families to the CCM1 locus on chromosome 7. The HCCVM seems to be a peculiar cutaneous vascular malformation associated with CCMs. These data strongly suggest that HCCVMs and CCMs in these families are due to the same genetic abnormality.