Moyamoya disease has been associated with renal artery stenosis, cerebral hemorrhage, and multiple cranial traumas. We report a unique case of moyamoya disease associated with polycystic kidney disease and eosinophilic granuloma. Although the etiology of moyamoya disease is unknown, a familial pattern of occurrence has been documented. Of particular importance is its presentation with polycystic kidney disease, an autosomal dominant disease, suggesting a hereditary component to the etiology of this unusual vasculitic disease.