The first Japanese autosomal dominant pedigree of familial retinal arteriolar tortuosity was presented with photographical documentation. The proband, a 7-year-old girl also had typical Coats' disease in her left eye. The fluorescein fundus angiogram revealed retinal telangiectasis and microaneurysms with dye leakage in her left peripheral eyeground and marked arteriolar tortuosity without dye leakage in posterior portions of both eyegrounds. Her father showed prominent retinal arteriolar tortuosity bilaterally, and her sister and paternal grandmother showed mild tortuosity of retinal arterioles in both eyes. The recently proposed hypothesis that the familial retinal arteriolar tortuosity is caused by the retinal microcirculatory disturbance consisting of increased resistance in the retinal capillary bed might explain the coincidental occurrence of retinal arteriolar tortuosity and Coat's disease in this report.