Aspirin Or Warfarin To Prevent Stroke

Inclusion Criteria: * TIA or non-severe stroke within 90 days prior to randomization (including day 90) * Modified Rankin score of \< 3 * High grade stenosis (50 to 99 percent) of a major intracranial artery (carotid artery, MCA stem (M1), vertebral artery,and basilar artery) documented by conventional angiography within 90 days prior to randomization (including day 90) * TIA or stroke is attributed to high grade intracranial stenosis * Age \> 40 years * Patient is able to follow an outpatient protocol(requiring monthly blood tests and clinic visits every four months for the duration of the study) and is available by telephone * Patient understands the purpose and requirements of the study, can make him/herself understood, and has provided informed consent Exclusion Criteria: * Extracranial carotid stenosis (\> 50 percent) ipsilateral to stenosis of the intracranial carotid artery or MCA (ie.tandem stenoses, either of which could have caused patient's symptoms) * Isolated stenosis of the anterior cerebral artery, posterior cerebral artery, MCA division, or a distal branch of the MCA * Intracranial or extracranial arterial dissection, Moya Moya disease, vasculitis, radiation induced vasculopathy, fibromuscular dysplasia * Presence of any of the following unequivocal cardiac sources of embolism: chronic or paroxysmal atrial fibrillation, mitral stenosis, mechanical valve, endocarditis, intracardiac clot or vegetation, myocardial infarction within three months, dilated cardiomyopathy, left atrial spontaneous echo contrast * A contraindication to the use of either warfarin or aspirin e.g. active peptic ulcer disease, active bleeding diathesis, platelets \< 100,000\*, hematocrit \< 30\*, clotting factor abnormality that increases the risk of bleeding, alcohol or substance abuse, severe gait instability, cerebral hemorrhage, systemic hemorrhage within the past year, severe liver impairment (SGOT \> 3x normal\*, cirrhosis), allergy to aspirin or warfarin, uncontrolled severe hypertension (systolic pressure \> 180 mm Hg or diastolic pressure \> 115mm Hg), positive stool guaiac that is not attributable to hemorrhoids, creatinine \> 3.0\* * Indication for intravenous heparin beyond randomization * A severe neurological deficit that renders the patient incapable of living independently * Dementia or psychiatric problem that prevents the patient from following an outpatient program reliably * Co-morbid conditions that may limit survival to less than five years * Pregnancy or female in age range of childbearing potential who is not using contraception * Enrollment in another study that would conflict with the current study * Excluded because difficult to measure percent stenosis of these small arteries, lesions are uncommon, and prognosis of patients - With these lesions is unknown \* on most recent test done within 90 days prior to randomization, including day 90