We studied two cases of mobile internal carotid artery lesions in symptom-free patients. Both cases were diagnosed by means of routine carotid duplex ultrasound scanning, and neither patient was operated on. With medical therapy with oral anticoagulants, the two lesions spontaneously disappeared without any clinical sequel, and no evidence of infarcts was shown by means of repeated computed tomography brain scans. After uneventful 2- and 3-year follow-up periods, there was no evidence of recurrence. This is the first published data on asymptomatic mobile carotid lesions and their natural history that shows a benign course in a long-term follow-up period. We suggest that a non-surgical approach may be considered selectively in high-risk symptom-free patients who have mobile and floating internal carotid artery lesions.