Contrary to a common view, ischemic stroke under the age of 45 is not rare. In the Lausanne Stroke Registry, more than 10% of the patients were within this age limit. Overall, in Occidental countries the causes of stroke in the young adult do not really differ from those in the older individual; it is only the relative frequency of stroke that is not the same. Cardiac embolism, arterial dissection, and migraine represent the most common etiologic factors, while atherosclerosis is much more unusual. The etiologic aspects and their therapeutic implications justify an active investigative attitude in young adults with recent ischemic stroke. After the acute phase of stroke, prognosis is reasonable.