Two cases of hereditary hemorrhagic telangiectasia (HHT) with neurological involvement are presented. One patient had multiple vascular malformations including telangiectasias of the brain, medulla, and spinal cord and a berry aneurysm of the internal carotid artery; she also had a large cerebellar abscess, presumably reflecting the presence of a pulmonary arteriovenous fistula. The second patient had an idiopathic subarachnoid hemorrhage. In more than 200 reported patients with HHT involving the nervous system, 61% had lesions seondary to a pulmonary arteriovenous fistula (cerebral hypoxemia, paradoxical and septic emboli, and brain abscess). The findings emphasize the need for early surgical correction of such fistulas. In 36% of the patients with neurological involvement and HHT, vascular malformations of the brain and spinal cord were documented, and in 3%, portal-systemic encephalopathy was noted. Multiple lesions were frequent. HHT should be considered a generalized vascular dysplasia (universal or systemic angiomatosis), and not simply a benign mucocutaneous disease.