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Background: Recent autopsy study showed a high incidence ofcerebrovascular lesions in Alzheimers disease (AD).To assess the impact of cerebrovascular pathology in AD, we used diffusion tensor imaging (DTI) to study AD patients with and without cerebrovascular lesions. Materials and Methods: Conventional and DTI scans were obtained from 10 patients with probable AD, 10 AD/V patients (probable AD with cerebrovascular lesions) and ten normal controls. Mean diffusivity (D) and fractional anisotropy (FA) values of some structures involved with AD pathology were measured. Results: D value was higher in AD patients than in controls in hippocampus and the cingulate gyrus. In AD/V patients, increased D value was found in the same structures and also in the thalamus and basal ganglia compared to controls. There was a significant difference of D value between AD and AD/V patients. FA value reduced in the white matter of left inferior temporal gyrus and in the bilateral middle cingulate gyrus in patients with AD/V compared with controls. The MMSE (mini-mental state examination) score significantly correlated with FA value in the right hippocampus (r=0.639, P＜0.019), in the right anterior cingulate gyrus (r=0.587, P＜0.035) and in left parahippocampal gyrus (r=0.559, P＜0.047). Conclusion: Cerebrovascular pathology had stronger impact on the D value than the AD pathology alone did. Elevated D value in thalamic and basal ganglia may contribute to cognitive decline in AD/V patients.Reduced FA values in AD/V patients may indicate that cerebrovascular pathology induced more severe white matter damage than the AD pathology alone did.