A 29-year-old female presented with Basedow's disease manifesting as sudden vomiting, diarrhea, fever over 38 degrees C, transient aphasia, and numbness in her extremities. These symptoms were considered due to cerebral ischemia at a local clinic. Magnetic resonance angiography indicated stenosis of the bilateral distal internal carotid arteries and the bilateral proximal anterior cerebral and middle cerebral arteries. Thyroid swelling and exophthalmos were observed. She was transferred to our hospital. Endocrine function tests showed hyperthyroidism. The diagnosis was Basedow's disease. Her symptoms disappeared after receiving intravenous drip infusion of fluid replacement, and antithyroid and antiplatelet medication. After she became euthyroid, cerebral angiography and magnetic resonance angiography revealed improvement of the stenosis of the cerebral arteries. Stenosis of the terminal portion of the internal carotid artery associated with Basedow's disease is extremely rare. Conservative treatment mainly including antithyroid medications for Basedow's disease, and antiplatelet drugs and intravenous replacement fluid for the ischemic manifestations should be the first choice of treatment unless immediate vascular reconstruction is necessary.