The authors describe the clinical results of surgical embolization in 55 patients with large cerebral arteriovenous malformations. Follow-up intervals ranged from 2 months to 14 years, averaging 4 1/2 years. The authors believe the procedure is safe in properly selected patients and is useful as a preliminary to direct surgical excision. It relieves associated headaches, and usually reverses or stabilizes a progressive neurological deficit. The potential for seizures probably is not altered. The incidence of hemorrhage following embolization is low for patients with no previous history of hemorrhage; however, the procedure does not reduce the likelihood of recurrence in patients with a prior history of hemorrhage.