Background: Information on the mechanism of recurrent stroke may help physicians treating patients with ischemic stroke. However, the mechanisms of recurrence in each stroke subtype are not well known, especially in Asians. Abstract:Objective: To compare the mechanisms of the index and recurrent stroke. Design: Analysis of data from a prospective acute stroke registry. Setting: University hospital. Patients: Using the clinical syndrome, diffusion-weighted imaging, and vascular studies, we divided 901 patients into 5 groups: large-artery atherosclerosis, cardioembolism, small-artery disease, parent-artery disease occluding the deep perforators, and no determined cause. The patients with large-artery atherosclerosis were subdivided into 2 groups: intracranial and extracranial. Main Outcome Measures: The mechanisms of recurrent vascular events (strokes or coronary heart disease) in subtypes of ischemic stroke were compared. Results: Ninety-three recurrent vascular events (86 strokes and 7 instances of coronary heart disease) were evaluated. The pattern of recurrent stroke differed for the intracranial and extracranial groups; unlike the patients with intracranial large-artery atherosclerosis, recurrent strokes in the extracranial group were often unpredictable with respect to the site of recurrence and degree of preexisting stenosis. None of the patients in the extracranial group had recurrences that were caused by intracranial large-artery atherosclerosis or vice versa. In patients with small-artery disease and stroke with no determined cause, intracranial stenosis was often found at the time of recurrence. Conclusions: From prognostic and therapeutic perspectives, patients with atherosclerosis should be divided into those with intracranial large-artery atherosclerosis and extracranial large-artery atherosclerosis. In addition, intracranial large-artery atherosclerosis may be important in the development of small-artery disease and stroke with no determined cause, especially in the population with a higher frequency of intracranial large-artery atherosclerosis. Background: Information on the mechanism of recurrent stroke may help physicians treating patients with ischemic stroke. However, the mechanisms of recurrence in each stroke subtype are not well known, especially in Asians. Abstract: Objective: To compare the mechanisms of the index and recurrent Settings: University hospital. Patients: Using the clinical syndrome, diffusion-weighted imaging, and vascular studies, we divided 901 patients into 5 groups: large-artery atherosclerosis, cardioembolism, Small-artery disease, parent-artery disease occluding the deep perforators, and no determined cause. The patients with large-artery atherosclerosis were subdivided into 2 groups: intracranial and extracranial. Main Outcome Measures: The mechanisms of recurrent vascular events (strokes or coronary heart disease) in subtypes of ischemic stroke were compared. Results: Ninety-three recurrent vascular events (86 strokes and 7 instances of coronary heart disease) were evaluated. The pattern of recurrent stroke differed for the intracranial and extracranial groups; unlike the patients with intracranial large-artery atherosclerosis, recurrent strokes in the extracranial group were often unpredictable with respect to the site of recurrence and degree of preexisting stenosis. None of the patients in the extracranial group had recurrences that were caused by intracranial large-artery atherosclerosis or vice versa. In patients with small-artery disease and stroke with no determined cause, intracranial stenosis was often found at the time of recurrence. Conclusions: From prognostic and therapeutic perspectives, patients with atherosclerosis should be divided into those with intracranial large-artery atherosclerosis and extracranial large-artery atherosclerosis. In addition, intracranial large-artery atherosclerosis may be important in the development of small-artery disease and stroke with no determined cause, especially in the population with a higher frequency of intracranial large-artery atherosclerosis.