We report a 64-year-old Japanese woman with recurrent ischemic strokes and progressive dementia without any cardiovascular risk factors. Her first stroke was at 45 years old, and she has a family history of ischemic strokes compatible with an autosomal dominant trait. Marked leukoaraiosis and multiple lacunar infarcts were shown on brain MR images, and no atherosclerotic changes were observed in her extra-and intra-cranial arteries by cervical arterial echography and intracranial MR angiography. Excluded other inherited or metabolic diseases causing leukodystrophy by examination of her blood samples, her disease was diagnosed as CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and lekoencephalopathy). We demonstrated granular osmiophilic materials (GOM) on the wall of small arteries from a biopsied peripheral nerve tissue specimen and detected a mutation Arg169Cys of Notch 3 gene. Many CADASIL patients have been reported and over 28 kinds of mutations of the Notch 3 were identified in western countries, while few CADASIL patients have been reported in Japanese people. Among them, eleven CADASIL families have been reported and only five mutations (Arg133Cys, Cys174Phe, Arg213Lys, Arg90Cys and Arg141Cys) have been determined so far. The mutation of Notch 3 in our patient was determined as Arg169Cys, and this is the first report on a Japanese patient with CADASIL due to this mutation.