There are rare reports of young women with moyamoya disease associated with Graves' disease; we are unaware of any previous reports of this association in prepubescent girls. We report a 10-year-old girl who presented with multiple bilateral strokes. Cerebral angiography demonstrated moderate to severe stenosis of her bilateral distal internal carotid arteries and proximal anterior and middle cerebral arteries, which was greater on the right. Thyroid function tests demonstrated suppressed thyroid-stimulating hormone and elevated thyroid hormone levels. Serum antiphospholipid antibody screen demonstrated mild elevations of antiocardiolipin IgG. Possible mechanisms predisposing individuals to concurrent moyamoya and Graves' disease are discussed.