✓ The clinical course of 50 patients with conservatively treated intracranial arteriovenous malformations (AVM's) was followed, most of them for more than 5 years. The average follow-up period was 13.4 years. The initial symptom was intracranial bleeding in 29 patients (58%) and seizure in 15 patients (30%). Small and deep-seated AVM's were associated with a high incidence of bleeding; however, repeated hemorrhages were not necessarily indicative of a poor prognosis. Children younger than 15 years had a better prognosis than adults. There was no correlation between pregnancy and bleeding. In the hemorrhage group, the incidence of rebleeding was 6.9% in the 1st year after initial rupture, 1.91% per year after 5 years, and 0.92% per year after 15 years. The overall incidence of rebleeding was 34.5% in the hemorrhage group. Of the 50 patients, 37 (74%) had a good clinical outcome, four (8%) had a fair outcome, and four (8%) had a poor outcome; five patients died.