✓The risk of hemorrhage in cavernous malformations (CMs) depends on lesion, host, and environmental factors. Anticoagulation therapy is a well-known risk factor for intracerebral bleeding, but the occurrence of hemorrhages in patients with CMs has not been reported. Low molecular weight heparin therapy is generally considered to be safe, although significant hemorrhagic complications have recently been reported. The authors report a case of intralesional bleeding in a CM after prophylactic anticoagulation therapy was administered in a patient with the familial form of the disease. The leaky endothelial structure of CMs may constitute an unexpected target of the vascular effects of heparin.