['The etiologic diagnosis of intracranial arterial occlusion is sometimes challenging because of the dynamic nature of acute stroke. We investigated whether short-term follow-up vascular imaging adds additional information to the differential diagnosis between intracranial atherosclerotic and embolic occlusion.', 'Acute ischemic stroke patients with symptomatic middle cerebral artery (MCA) occlusion on MR angiography (MRA) within 24h of symptom onset were included. Follow-up MRA was performed 5-7days after stroke onset. Stroke subtypes were independently determined at baseline and follow-up MRAs based on clinical, laboratory and imaging findings.', 'In the 108 included patients, the most common etiologic subtype of initial stroke was intracranial large artery atherosclerosis (ICLAA) in 70 patients, followed by cardioembolism in 29 and other causes in 9. On follow-up MRA, 32 (29.6%) patients showed either significant or complete recanalization. Of these, 10 had been originally diagnosed with ICLAA, but were reclassified as a cryptogenic mechanism after follow-up MRA. Multiple logistic regression analysis showed that the presence of coexisting arterial atherosclerosis (odds ratio [OR], 6.91; 95% confidence interval [CI], 2.67-17.91; p<0.001); the absence of large territorial infarction (OR, 4.06; 95% CI, 1.39-11.85; p=0.010); and smoking (OR, 2.54; 95% CI, 1.028-6.29; p=0.043) were significantly associated with a final diagnosis of ICLAA.'] Is evaluation of early dynamic changes of intracranial arterial occlusion useful for stroke etiology diagnosis?