Serious morbidity and hyperemic states continue to complicate the treatment of certain intracranial arteriovenous malformations (AVMs). Clinical and radiographic characteristics of 62 patients treated over 3 years were analyzed to determine if hyperemic complications (HCs) (defined as unusual perioperative edema or hemorrhage) and outcome could be predicted. Twenty-five (40%) of the patients were less than 30 years old, 28 (45%) were between 30 and 50, and 9 (15%) were more than 50. A history of hemorrhage was found in 48%, and 34% presented with progressive deficits. Thirteen (21%) developed evidence of HCs; 51 (82%) ultimately had a good outcome, 4 (6%) had a poor outcome, and 7 (11%) died. The incidence of HCs was higher in patients whose AVMs recruited perforating vessels (53%) than those without (7%) (P less than 0.001). The presence of preoperative angiographic steal carried a 35% risk of HCs whereas its absence carried a 13% risk (P less than 0.05). The sum of the diameters of the feeding vessels was also predictive (P less than 0.05). Outcome was clearly age-related: good outcome was achieved in 92% of the patients less than 30 years old, 86% of those 30 to 50, and 44% of patients older than 50 (P less than 0.05). Left hemispheric AVMs showed less morbidity than right (P less than 0.05) as did those without perforating vessel recruitment (P less than 0.07). HCs had a dramatic impact on outcome with 92% of patients without HCs having good outcome and 46% of those with HCs recovering well (P less than 0.001).