We report a case of Prader-Willi syndrome (PWS) complicated with juvenile 
stroke. The patient is a 19-year-old man with right hemiplegia, who has had a 
history of non-insulin-dependent diabetes mellitus (NIDDM) for ten years. The 
diagnosis of PWS was confirmed genetically by the method of fluorescence in situ 
hybridization which showed the deletion of chromosome 15. His brain MRI revealed 
abnormal signal intensities in the left basal ganglia and around the right 
trigone of the lateral ventricle. Angiographic examination showed occlusions of 
bilateral proximal middle cerebral arteries with basal moyamoya vessels. The 
left vertebral artery was also occluded at its origin. Only a few cases of PWS 
complicated with stroke have been reported before and, to date, there has been 
no case with arterial occlusion similar to our case. Though the cause of these 
arterial occlusions is unknown, it may be related to arteriosclerosis following 
NIDDM.