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Transient global amnesia (TGA) is the inability to retain new information and to recall past events during a period of minutes or hours. Its etiology is unclear, and flow disturbances in the mesial temporal lobes secondary to venous congestion have been proposed as a potential cause. Ultrasonographic evaluation of the internal jugular vein (IJV) has demonstrated valvular insufficiency in TGA. The prevalence of valvular insufficiency in the IJV in patients with TGA was assessed. Subjects without TGA of similar sex, age, and vascular risk factor profiles served as controls.A group of 142 patients with a clinical diagnosis of TGA within 7 days of the clinical event and 40 controls were prospectively evaluated. Venous Doppler examination of both IJVs was performed at baseline and after a manometer-controlled Valsalva maneuver. Valvular insufficiency was diagnosed when there was reflux for >0.8 seconds during the Valsalva maneuver.Valve insufficiency was found in at least one jugular vein in 113 of 142 patients with TGA (79.5%) and in 10 of 40 controls (25.0%), P<0.01. The right side was affected more often than the left side, P<0.01, and 26.8% of the patients had bilateral incompetence.Patients with TGA have a high prevalence of IJV valve insufficiency. This finding may have pathophysiologic implications. Doppler evaluation of the IJVs with dynamic maneuvers may help in the evaluation of this usually benign condition.