Aim To analyze the risk factor of asymmetric leukoaraiosis(LA) and explore its incidence and its pathogenesis. Methods 266 consecutive patients elder than 40 years were included prospectively.Their clinical data were analyzed respectively.All of them had accepted a magnetic resonance lmaging(MRI) and a Ultrasonic examination.The white matter hyperintensities(WMH) volume of fluid attenuated inversion recovery(FLAIR) were quantified with a semi-automated method,Leukoaraiosis patients with a ratio of WMH volumes in heavy side and in light side >1.5 were considered as asymmetric LA,and numbers of lacunes were counted. Local factors were records for the analysis. Results 32 cases of asymmetric leukoaraiosis were found,the incidence of asymmetric LA was 12.03%.Comparing the risk factor of asymmetric LA patients and symmetric LA,the two groups had significant difference in age,history of hypertension,diabetes,carotid artery plaques/stenosis,ischemic stroke,and the heavy side of asymmetric LA had more lacunar infaction,higher Crouse scale.Binary Logistic regression showed age,history of hypertension,lacunar infarction and carotid artery plaques/stenosis were included in the model. Conclusion The risk factors for asymmetric LA are age,history of hypertension,lacunar infarction and carotid artery plaques/stenosis.