A 29-year-old Caucasian male died from massive cerebral infarction due to unilateral occlusion of the terminal internal carotid artery. The carotid occlusion was secondary to subendothelial fibrous tissue proliferation which was associated with a considerable mononuclear cell infiltration of the carotid wall, characterised as T cells by immunoperoxidase methods. Angiography showed vascular network at the base of the brain compatible with Moyamoya disease. We suggest that the pathogenesis of Moyamoya-like disease in our patient involved a T-cell-mediated attack to a vascular antigen.