&NA;The availability of transcranial Doppler sonography has resulted in an easy, noninvasive, reproducible, and highly reliable method for evaluating the flow characteristics of carotid‐cavernous sinus fistulas. It also allows the follow‐up of the effect of different interventional measures, specifically, embolization with detachable balloons. An illustrative case is reported, in which the findings of serial transcranial Doppler sonograms are correlated with findings on computed tomographic scans and angiograms. The impact of our findings on future approaches to the hemodynamic classification of these acquired vascular shunts is discussed. (Neurosurgery24:749‐753, 1989)