A seventy-year-old woman suffered a fatal cerebellar rehemorrhage from a large venous aneurysm associated with a dural arteriovenous malformation (AVM) of the posterior fossa. The malformation, fed by branches of the right vertebral, occipital and middle meningeal arteries, had a nidus in the transverse sinus wall with a pedunculated extension reaching the pial surface of the adjacent cerebellum, from where the malformation drained exclusively into an aneurysmal cerebellar vein. There was no associated venous sinus obstruction. Histopathological examination of the venous sinuses, arteriovenous malformation and venous drainage is described and these findings as they relate to the pathogenesis of dural AVMs are discussed. Vascular malformations of the dura mater do not appear to be a single clinical or pathological entity. The serious risk of hemorrhage from a parenchymal venous aneurysm is emphasized.