A 16-year-old girl with Down syndrome, moyamoya disease, and history of a previous stroke presented with acute onset of left hemiparesis and elastosis perforans serpiginosa. Elastosis perforans serpiginosa in a patient with Down syndrome and moyamoya disease is a novel finding. Development of elastosis perforans serpiginosa in association with progressive vaso-occlusive disease may be a biological marker of progression of moyamoya disease.