Duplex sonography has been used to non-invasively diagnose carotid artery disease and to follow up patients with this disease. In carotid artery disease, carotid mobile thrombus and dissection are rarely detected by duplex sonography in patients with cerebrovascular events. In particular, carotid dissection occurs when a small tear forms in the tunica intima and makes 2 lumens in the carotid artery, including true and false lumens. This study reports 3 rare cases of carotid mobile thrombus, spontaneous carotid dissection, and carotid dissection in Takayasu arteritis.