Longer existing atherosclerotic lesions may contain calcifications; lamellar bone rarely develops within them. A 59-year-old man was referred with a progressive stroke. A high-grade stenosis of the left common carotid artery, formed by an ulcerating atherosclerotic plaque with a free-floating thrombus, was detected on angiography. An urgent endarterectomy was performed. Surprisingly this plaque contained pieces of lamellar bone, proved by histologic examination.