Alzheimer disease (AD) is pathologically characterized by cortical atrophy. Changes in the white matter and their relation to the pathogenesis of AD remain to be studied. To quantitatively investigate the integrity and organization of white matter fiber tracts in patients with AD, we used diffusion tensor (DT) imaging to study the diffusion anisotropy of white matter regions. DT imaging was performed using a 3.0 Tesla magnetic resonance scanner in ten probable AD patients with no or only mild changes in the white matter in T2 weighted magnetic resonance imagings and ten group-matched controls. The values of fractional anisotropy were significantly lower in the temporal subcortical white matter, posterior part of the corpus callosum, and anterior and posterior cingulate bundles in patients with AD compared with controls. Possible relationships of these selective impairments in the white matter with pathological changes in the posterior cerebral cortices and hippocampus were discussed.