Patients with arteriovenous malformations of the brain, who are subject to disabling or fatal recurrent hemorrhage, seizures, severe headache, and progressive neurologic deficits, may be considered unsuitable for conventional therapies (craniotomy with excision or embolization), usually because of the location, size, or operative risk of the lesion. We have treated such patients with stereotactic Bragg-peak proton-beam therapy and report the follow-up of 74 of the first 75, 2 to 16 years after treatment. Proton-beam therapy is intended to induce subendothelial deposition of collagen and hyaline substance, which narrows the lumens of small vessels and thickens the walls of the malformation during the first 12 to 24 months after the procedure. Two deaths from hemorrhage occurred in the first 12 months after treatment, but no lethal or disabling hemorrhages occurred after this interval. Seizures, headaches, and progressive neurologic deficits were in most cases arrested or improved. Bragg-peak proton-beam therapy appears to be a useful technique for treatment of intracranial arteriovenous malformations, especially those that are unsuitable for treatment by other methods.