Diffusion-weighted MR imaging was performed in 5 control subjects and 8 patients with Alzheimer's disease(AD). The mean values of fractional anisotropy(FA) were calculated in the genu and splenium of the corpus callosum, and anterior and posterior cerebral white matter. The FA value of the posterior white matter in patients with AD was significantly lower than that of controls. Fractional anisotropy may be useful in the diagnosis of AD.