BACKGROUND: The natural history of cranial dural arteriovenous fistulas (DAVFs) without cortical venous drainage (i.e., benign DAVF) is considered a potential predictor of a benign clinical course. We report a case of intracerebral hemorrhage due to the conversion from a benign to an aggressive DAVF during 10 months of conservative therapy, which, to the best of our knowledge, is the first reported case of its kind. CASE DESCRIPTION: A woman in her 70s without neurological symptoms was diagnosed with DAVF of the right transverse-sigmoid sinus with Borden type I. After conservative therapy was maintained for 10 months, she had a slight headache without neurological deficits and magnetic resonance imaging revealed intracerebral hemorrhage in the right temporooccipital area. Routine laboratory tests revealed a slight elevation of D-dimer. Emergent digital subtraction angiography demonstrated new cortical venous drainage and stenosis of the venous outlet. The refluxed cortical vein and right transverse-sigmoid sinus including fistulas were occluded with coils via transvenous embolization. She had no neurological deficits in the postoperative state. CONCLUSIONS: Conversion to aggressive DAVF in this patient was probably due to spontaneous stenosis or thrombosis of the venous outflow. Intracranial hemorrhage can occur within 1 year from the detection of benign DAVFs, and elevated D-dimer may predict the conversion to aggressive DAVFs.