A subgroup of patients initially treated by radiosurgery underwent surgical resection because of recurrent hemorrhage or neurological deterioration. In a retrospective study, we want to analyze the clinical features of these patients and evaluate the effect of microneurosurgery in such rare constellations. Moreover, we hope to find answers about failure of radiation therapy in these cases by correlation of radiobiological and histopathological data. Over a 16-year-period, eight patients with cerebral arteriovenous malformation (AVM) underwent surgical resection, who previously were treated by radiosurgery. The mean duration between radiation therapy and final resection was 7 years. Preoperative evaluation revealed Spetzler-Martin grade III (n=5) and IV (n=3) AVMs. Histological examination was achieved in all resected lesions. Mean neurological follow-up was 14 months. Indications for surgical resection were intracerebral hematoma, progressive neurological deficit, and epilepsy. In comparison to the initial angiographic study before radiation therapy, preoperative angiography revealed newly developed "en passant" feeding vessels and stenosis of the main venous drainage in some patients. The mean Rankin score for all patients was 2.75 before and 3.25 after surgical resection. Postoperatively, three patients (38%) developed neurological deterioration. Histological examination of the resected tissue revealed significant radiation-induced pathology in six patients. We did not see correlation between radiation doses and severity of histolopathological radiation-induced changes. Postoperative angiography confirmed total AVM resection in all patients. AVMs insufficiently treated by radiation bear an increased surgical risk. Often, angiographic studies revealed a more complicated morphology. Microsurgical resection was extremely challenging and led to unfavorable outcomes in many of the patients.