Between May, 1988, and August, 1991, 80 patients with arteriovenous malformations (AVM's) were treated radiosurgically at the University of Florida. A mean dose of 1650 cGy was directed to the periphery of the lesion, which almost always corresponded to the 80% isodose line. The mean lesion diameter was 23 mm. Seventy-six patients were treated with one isocenter. Angiography, performed at 1 year after radiosurgery in 41 of the 48 eligible patients, revealed an overall complete thrombosis rate of 39%. The 1-year thrombosis rate was highest in those patients with relatively small AVM's. Angiography was performed at 2 years posttreatment in 21 of the 25 eligible patients, demonstrating an overall complete thrombosis rate of 81%. This incidence did not correlate with lesion size: that is, large lesions (up to 35 mm in diameter) seemed just as likely to thrombose. Two patients (2.5%) experienced hemorrhage at some time after radiosurgical treatment, and both recovered. Two patients (2.5%) have sustained mild, but permanent, radiation-induced neurological complications.