Chronic kidney disease (CKD) is a major risk factor for poor prognosis in patients with cardiovascular diseases.We previously showed that renal artery stenosis (RAS) was often found in patients with cardiovascular diseases such as myocardial infarction. The aim of the present study was to evaluate the incidence and risk factors of RAS in patients with stroke or severe carotid artery stenosis, (l) From 2, 167 autopsy patients during the 17-year period between 1980 and 1997, we studied 346 cases with stroke. RAS was found in 36 patients (10.4%), and the patients with RAS were older and had worse kidney function. Multiple logistic regression analysis identified kidney function, hypertension, and carotid artery stenosis as independent predictors of RAS. (2) From February to August 2006, 41 consecutive patients with severe carotid artery stenosis were admitted to the department of Neurosurgery of National Cardiovascular Center. Kidney function, urinary albumin excretion and renal artery duplex scanning were performed in all patients. They were classified into two groups according to the findings of renal artery duplex scanning, 11 patients with RAS and 30 patients without RAS. We evaluated the differences in clinical findings and renal function between the groups and clarified the risk factors for RAS. In the patients with RAS, smoking and incidence of cardiovascular diseases were evident, and kidney function was impaired significantly compared with the patients without RAS. Multivariate logistic regression showed that smoking, the presence of cardiovascular diseases and kidney function were significant clinical predictors for RAS. (3) Carotid endarterectomy was performed in 42 patients with RAS (n = 11) and without RAS (n = 3l) in our hospital. Transient increase of serum creatinine and decrease of urine output was observed in the patients with RAS. In conclusion, RAS was frequently detected in the patients with stroke or severe carotid artery stenosis. The risks of RAS were smoking, the presence of cardiovascular diseases and kidney dysfunction. Since RAS was the underlying cause of hypertension and renal failure, it is important to consider the presence of RAS in patients with stroke or carotid artery stenosis.