The introduction of transcranial Doppler ultrasonography (TCD) has made it possible to examine blood flow characteristics in carotid-cavernous sinus fistulae (CCSF) in a noninvasive, relatively simple, and reliable way. This study investigated the usefulness of TCD in the diagnosis and follow-up of various CCSF subtypes. We found characteristic TCD findings associated with high-flow CCSF, but perhaps more importantly, found this technique to be an excellent tool also for detecting and following treatment results in low-flow CCSF. The low-flow fistulae exhibit less specific clinical signs and are harder to distinguish using the noninvasive radiological methods of computed tomography (CT) and magnetic resonance imaging (MRI). The impact of our findings on future approaches to the diagnosis and follow-up of these different types of acquired vascular shunts is also discussed. The conclusions were as follows: a) TCD parameters (blood flow velocity and pulsatility index) for CCSF are specific, and are thus valuable in the hemodynamic assessment of these lesions. b) Since dural CCSF feature more subtle hemodynamic changes and CT and MRI findings may be normal, these cases pose diagnostic challenges. In these situations, TCD reveals specific diagnostic findings and allows the examiner to determine whether cerebral angiography is indicated.