White matter damage and its contribution to clinical manifestations in patients with dementia have been increasingly recognized. To explore white matter changes in different types of dementia, we examined brain water diffusivity with diffusion tensor imaging (DTI). We measured fractional anisotropy and mean diffusivity of multiple white matter regions in patients with amnesic mild cognitive impairment (MCI, n=10), Alzheimer's disease (AD, n=30), subcortical ischemic vascular dementia (SIVD, n=18), frontotemporal dementia (FTD, n=7), and control subjects (n=20). We performed pairwise comparisons in each region of interest between patients and controls. MCI patients showed diffusion tensor change (DTC) in the left anterior periventricular (PV) area, possibly in the right posterior PV area, and the genu of the corpus callosum. AD patients showed DTC in the corpus callosum, and in frontal and parieto-occipital subcortical and anterior PV areas. In SIVD patients, DTC occurred in the genu of the corpus callosum, and in bilateral frontal subcortical and PV areas. FTD patients differed from controls in showing DTC in the temporal and frontal subcortical areas, the genu of the corpus callosum and PV areas. The degree of DTC correlated with the clinical severity of dementia as assessed by the clinical dementia rating (CDR). Mean diffusivity was diffusely and positively associated with the CDR scores. Fractional anisotropy of the PV areas was negatively associated with the CDR scores, suggesting a critical role of the lateral cholinergic pathways.