OBJECTIVE The etiologic mechanisms of young ischemic stroke in Chinese are largely unknown. This work thus studied the etiologies of young ischemic stroke in Taiwan Chinese and made a comparison with previous reports. METHODS From January 1997 to October 2001, a total of 264 consecutive young ischemic stroke patients (18 to 45 years old) were admitted to the Department of Neurology in our hospital. The risk factors for stroke and the distribution of stroke subtype were studied. The vascular ultrasound and angiographic findings of these patients were also studied. RESULTS The sample contained 188 men and 76 women. Cerebral infarction was diagnosed in 241 patients and transient ischemic attack in 23 (8.7%). Regarding stroke subtype, stroke of small-vessel occlusion was diagnosed in 20.5% of cases, large-artery atherosclerosis in 7.2%, cardioembolism in 17.8%, other determined etiology in 22.3%, and undetermined etiology in 23.5%. The 4 most common risk factors were hyperlipidemia (53.1%), smoking (49.8%), hypertension (45.8%), and family history of stroke (29.3%). Twenty-three patients (9.6%) had significant stenosis (> or =50%) of the carotid (7.5%) and vertebral arteries (2.1%), the most common cause of which was dissection (60.9%). Forty-five patients (26.5%) had significant intracranial stenosis with 18.8% in the carotid and 10.6% in the vertebrobasilar system, and 5 (2.9%) had stenosis in both systems. Premature atherosclerosis (33.3%) was the most common cause of intracranial stenosis. CONCLUSIONS Our study found that strokes of other determined etiology and undetermined etiology were most common among the sample group, and a battery of extensive examinations is indicated to elucidate the etiology for further stroke prevention. Intracranial stenosis is more common than extracranial stenosis in both the carotid and vertebrobasilar systems.