Atheromatosis frequently develops in the carotid bifurcation, leading to significant stenoses of the internal carotid artery. The associated risk of stroke reaches 20-25% during the first three years for a high-grade symptomatic stenosis and 2-3% per year for a high-grade asymptomatic stenosis. The diagnosis of carotid stenosis is made after occurrence of a cerebral ischemic event or during an angiologic examination, mainly using Doppler/Duplex-sonography. Ultrasonography also enables an accurate determination of the grade of stenosis and accordingly the risk of stroke. Non-invasive MR- or CT-angiography is presently preferred to digital subtraction angiography to confirm the sonographic findings and prepare for an intervention. The intervention has to be decided individually for each patient. It is mandatory that the estimated risks of operation + best medical therapy be significantly lower than the risks of medical therapy alone; otherwise, the benefit of the intervention is lost for the patient. Only the mortality and major morbidity are taken into consideration to estimate the risks of an intervention. Local and systemic complications are transitory and do not influence the final outcome. A high-grade symptomatic stenosis (70-99%) should be operated upon whenever possible. A middle-grade symptomatic stenosis (50-69%) is treated operatively only if the associated risk of stroke is estimated to be high. A high-grade asymptomatic stenosis is operated upon only if the estimated perioperative risks are very low (< 3%). A middle-grade asymptomatic stenosis as well as low-grade stenoses (< 50%) should not be operated, but treated with the best medical therapy available. Carotid endarterectomy is established as method of first choice to treat a carotid artery stenosis. A major complication rate as low as 1% can be expected in experienced centres. The long-term results of carotid endarterectomy are well documented and the incidence of restenosis is very low. Endovascular angioplasty with stenting is increasingly performed as an alternative to the open operation. Presently, the scientific evidence is still lacking to recommend this method as primary therapy; however, progress in the field is constant and we expect new technical improvements which should increase the safety and efficacy of the procedure in the near future.