The authors report the de novo occurrence and treatment of an arteriovenous lesion within an anaplastic oligodendroglioma in a patient with previously unremarkable brain imaging. Intracranial arteriovenous malformations (AVMs) are believed to be congenitally acquired lesions, and their association with brain neoplasms is extremely rare. Diagnostic imaging revealed a mass lesion with large arteriovenous shunts and a vascular nidus mimicking a true AVM. Histological and immunohistochemical testing showed an anaplastic oligodendroglioma mixed with an AVM. The clinical, radiological, and operative data are reviewed, as are the histopathological findings. To the authors' knowledge this is the first case of de novo occurrence of an arteriovenous lesion with large shunts and a vascular nidus within an anaplastic oligodendroglioma.