We review seven patients with intracranial dural arteriovenous fistulae (ICDAVF), each altering the initial type of venous drainage to one with a higher grading during long-term follow-up. Five were discovered due to symptoms of intracranial hypertension, two due to changes in tinnitus and one case following subarachnoid haemorrhage. In five cases, cortical venous drainage developed during the follow-up period. Three different mechanisms were observed: stenosis or thrombosis in the draining veins in 4 cases: increased arterial flow in 2; and the appearance o a new fistula site or extension of the initial shunt in 2. Type I and type II a fistulae which are not completely cured, require both close clinical observation and Doppler examinations in the follow-up period. Any charge in the clinical pictures indicates a repeat angiogram. Stenosis of the venous drain-age, forecasting later worsening in the venous outlet, requires more thorough angiographic follow-up.