Hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber disease) is a syndrome characterized by the presence of mucocutaneous telangiectasia, recurrent hemorrhage (epistaxis from nasal telangiectasia is by far the most common form), and hereditary occurrence. Hereditary hemorrhagic telangiectasia is thought not to be a simple mucocutaneous disease but a generalized vascular dysplasia, because multiple visceral organs and systems, including central nervous system, are involved. But, an involvement of the central nervous system in this disease is rare. We experienced a case with cerebral arteriovenous fistula that was also diagnosed as possible hereditary hemorrhagic telangiectasia. In this communication this case is reported and the relevant literature is reviewed. A 30-year-old male, who was diagnosed as having possible hereditary hemorrhagic telangiectasia, was found to have abnormal findings on head CT scan during the evaluation of his disease. So he was admitted to the neurosurgical department for further examination. He was also known to have pulmonary arteriovenous fistula (11.5% arteriovenous shunt) and secondary polycythemia (RBC 533 X 10(4)/mm3, Hb 17.6 g/dl, Ht 51%). His past medical history was noteworthy for several episodes of epistaxis since childhood. His uncle had also pulmonary arteriovenous fistula and was operated on at another hospital. On admission, he was alert and showed normal neurological findings. Routine x-ray of the skull showed abnormal thinning of the skull in the right parietal region. Computed tomograms showed a lobulated high-density mass in the right parietal lobe which was homogeneously enhanced after bolus injection of contrast material. Right carotid angiograms disclosed a dilated aneurysmal vein in the parietal lobe.(ABSTRACT TRUNCATED AT 250 WORDS)