It is known that various complications are observed in patients with Down syndrome. We report a 1-year-old girl with Down syndrome who developed moyamoya syndrome presenting multiple cerebral infarction. Her chief complaints were recurrent convulsion and weakness on the left side of the body. Brain CT and MRI demonstrated multiple abnormal signals, and the lesion was diagnosed as multiple cerebral infarction. Since obstruction of the right anterior and middle cerebral arteries was observed by MRA, the patient was diagnosed with moyamoya syndrome. Moyamoya syndrome accompanied by Down syndrome advances in the early stage, and since it often occurs with cerebral infarction, the timing of its early diagnosis by MRA and caution of cerebral infarction are important. However, no guidelines for the control of moyamoya syndrome have been established in Down syndrome. Therefore, MRA should be performed in patients in whom moyamoya disease is suspected, because no useful method for the prevention of this complication disease has established
