A 35 year-old Caucasian male with history of acute lymphoblastic leukemia with peripheral blood stem cell transplantation 6 years ago presented with 3 month history of gradually worsening headaches with photophobia and one week history of right arm numbness. Exam was notable for right arm drift. Brain MRI revealed multifocal enhancing and diffusion restriction lesions with T2/FLAIR hyperintensity in bilateral frontal, parietal, and right parieto-occipital lobes. Differentials included stroke and post-transplant leukoencephalopathy. Rheumatological, infectious and malignancy workup was unrevealing except for positive serum EBV PCR. CT angiography (CTA) head and neck showed mild stenosis of right cervical internal carotid artery (ICA) and normal left ICA. Three days later patient developed acute left side weakness. Follow-up MRI showed new multifocal diffusion restriction lesions suggestive of stroke. Repeat CTA showed complete left ICA occlusion and 80% right ICA stenosis confirmed with digital subtraction angiography (DSA). MRA head and neck revealed diffuse vessel wall thickening and enhancement of bilateral ICAs, basilar, vertebral and left middle cerebral arteries suspicious for vasculitis. Transthoracic echocardiogram showed ejection fraction of 30%. The patient was empirically treated with 3 days of intravenous methylprednisolone and one dose of cyclophosphamide. He responded well to treatment. Follow-up DSA six days post treatment demonstrated reversal of right ICA stenosis from 80 to 20% and did not require stenting. Left ICA occlusion was unchanged. Ejection fraction improved to 60% from 30%.