Internal carotid artery dissection is an increasingly recognized cause of cerebrovascular events. The diagnosis is conventionally established on the basis of characteristic clinical symptoms and arteriographic findings. However, the presence of characteristic hemodynamic features detected by ultrasound may already suggest the diagnosis, even in atypical cases. This is demonstrated in 16 (76%) of 22 patients with internal carotid artery dissection. An intense systolic low-frequency Doppler signal of alternating flow direction accessible in the neck, either along the extent of a luminal tapering stenosis or proximal to a severe obstruction at the skullbase, indicated this diagnosis. Resolution or decreasing stenosis may similarly be diagnosed noninvasively, as shown by results from subsequent arteriograms in 14 patients (64%). This occurred suddenly during sequential follow-up between 2 days and 30 weeks (mean, 6 weeks) after the diagnosis was made.