Relapsing polychondritis is a rare autoimmune disease characterized by inflammation of cartilaginous tissues. It may be associated with systemic and cerebral vasculitis and exceptionally with ischemic stroke. Brain infarction associated with internal carotid artery thrombus, in a setting of relapsing polychondritis, has never been reported. We present a 52-year-old man without any known risk factors for stroke, treated with prednisone and azathioprine for relapsing polychondritis, who presented a minor left hemisphere stroke. Ultrasound of the neck vessels revealed an isoechogenic thrombus in the left internal carotid artery superimposed on a smooth moderately stenosing isoechogenic atheroma of the carotid bulb. The patient was treated with high-dose tinzaparin and was followed with serial ultrasound. After 16 days, the thrombus demonstrated a hypoechogenic core surrounded by a hyperechogenic rim and the following day it resolved completely. Thrombus formation on a small unruptured plaque may reflect involvement by relapsing polychondritis of the intimal proteoglycans that hold a role in the development of atheromatosis.