The authors report the case of a 39-year-old woman with type I neurofibromatosis who presented a right incomplete proportional hemiplegia which progressively worsened over a 6-month period. Left hemispheric atrophy with heterogeneous features, predominant in the temporoparietal region, was revealed by computerized tomography. Atrophy was associated with diffuse vascular lesions in the distal part of the left sylvian and anterior cerebral arteries, leading to major cortical hypoperfusion. Vascular examination showed no hypertension nor any sign of arterial involvement in another region. This case illustrates the nature of vasculopathy associated with neurofibromatosis. Its expression is polymorphous, with lesions inducing stenosis (the most common ones), aneurysmal lesions or veritable angiodysplasias (either hypo- or hyperplastic). The vascular expression of neurofibromatosis is often overlooked. However, in the presence of an inexplicable occlusive or aneurysmal vasculopathy, it is advisable to search for signs of neurofibromatosis since ill-defined forms exist.