This research examined the neuropsychological functioning of demented patients with periventricular and deep white matter alterations. Thirty-three outpatients with NINCDS-ADRDA probable Alzheimer's disease (AD) and 27 outpatients with probable/ possible ischaemic vascular dementia (IVD, Chui et al., 1992) associated with periventricular and deep white matter alterations matched for age, education, level of dementia, and functional disability were studied. White matter alterations were measured using a 40-point scale previously described by Junque et al. (1990). Subjects with cortical CVAs were excluded. On executive control tests, IVD subjects made more preservations on tests of mental control and response set, and produced fewer responses on phonemic controlled oral word association tests (letters: F,A,S). IVD subjects also made more preservations and graphomotor errors on clock drawings. On the California Verbal Learning Test the IVD group performed better than AD subjects on the short delay free recall test condition, the recognition discriminability index, and made fewer intrusion errors on both free and cued recall conditions. We conclude that neuropsychological assessment can differentiate AD from IVD associated with white matter alterations, and that the neuropsychological profile of demented subjects with significant periventricular and deep white matter alterations is similar to other subcortical dementing illnesses.