Hereditary hemorrhagic telangiectasia (HHT) also known as Osler-Weber-Rendu syndrome is one of the most common autosomal dominant disorders. Three different phenotypes of vascular malformations have been differentiated in the central nervous system (CNS), including large fistulae characterized by a direct arteriovenous shunt without nidus but with an ectatic draining vein, small arteriovenous malformations (AVMs) with a nidal size between 1 and 3 cm, and micro-AVMs with a nidus smaller than 1 cm. Cerebral ischemic manifestations are severe complications of the paradoxical embolism in patients with HHT. Apart from paradoxical embolism, two other mechanisms could favor cerebral ischemic manifestations in HHT patients, including blood hyperviscosity related to polycythemia and air embolism from the lung to the brain. Prevalence of cerebrovascular malformations in HHT is estimated at 5% using only computed tomography (CT), but it increases up to approximately 20% when magnetic resonance imaging (MRI) is performed.