A 65-year-old man with Rendu-Osler-Weber syndrome was admitted to the department of brain surgery at our hospital because of left hemiplegia and a right cerebral mass seen on a computerized tomogram of the brain. A brain abscess was found during surgery. Then the patient had pneumonia. He received antibiotics and recovered, but his PaO2 remained low. He was transferred to our department for evaluation of hypoxia. Thoracic computerized tomography showed a nodular lesion connected to a vascular shadow. Angiographic examination showed a pulmonary arteriovenous fistula and other vascular abnormalities. He was not dyspneic or cyanotic, but his hypoxia, low diffusing capacity, and brain abscess were thought to be caused by the pulmonary arteriovenous fistula. The fistula was embolized with coils via a percutaneous catheter, after which oxygenation and diffusing capacity improved.