Stroke in the young is rather rare. The absolute proportion of juvenile stroke is strongly linked to the structure of the population. In western European countries, with a high prevalence of old and very old people, less than 5% of strokes occur in subject under 45 years. The incidence is about 10 in 100,000 in several Italian studies. In Italy, about 3,300 new cases of juvenile stroke occur each year. Higher incidence rates have been found in the United States and developing countries. Subarachnoid hemorrhage prevails in young cases, compared with the total population of stroke patients. In the subgroup of patients with cerebral infarction, inter-atrial septum defects and inherited thrombophilic disorders seem to play an important role.