Two cases of a posterior fossa dural arteriovenous malformation associated with a lateral sinus thrombosis are reported. In the first case, a right tentorial meningioma develops at the end of the superior sagittal sinus and on the transverse sinus which are occluded. A cranial bruit, heard by the patient four months after the surgical removal of the tumour, brings up a dural fistula supplied by the occipital, middle meningeal and pharyngeal arteries and drained away by cervical and cortical veins. Many attempts of extirpation and radiological embolization stop the bruit. In the second case, an increased intracranial pressure mixes up with an aphasia. A continuous emission doppler examination and a CT scan make likely a dural fistula. The malformation, which is associated to a left sigmoid sinus thrombosis, is fed by the occipital and middle meningeal arteries and drained by cortical veins to the cavernous sinus. The occipital artery ligation and a by-pass between the lateral sinus and the internal jugular vein cure the patient with a very good patency of the venous graft that holds up two years after. A few cases of the literature show the succession of the two vascular lesions and prove the primitive occurrence, either of the sinus occlusion, or of the dural fistula. A venous thrombosis might cause a fistula by the opening of physiological shunts of the dura-mater which consequently deviates the blood into the cortical veins, brings down the increased intracranial pressure and stops the thrombosis to spread.(ABSTRACT TRUNCATED AT 250 WORDS)