The relationship between quantitative measurements of brain white-matter hyperintensity (WMH), assessed by magnetic resonance imaging and neuropsychological functions, was explored in demented patients and healthy aged individuals with and without WMH in 12 brain regions. The prevalence of WMH was significantly higher in vascular dementia compared with Alzheimer's disease, especially in posterior periventricular regions. Results showed no difference in any neuropsychological measurement between healthy aged adults with and without WMH. The demented patients with WMH were more impaired in tests of visuoconstruction, attention, finger-motor speed, and latency of tactile identification of objects compared with patients without WMH. These impairments were related mainly to posterior periventricular WMH. There was no relationship between WMH and global cognitive functioning in the demented patients. The degree of WMH was related to age and blood pressure. The data suggest that specific regional WMH may result in specific neuropsychological impairments.