Regional areas of the corpus callosum (CC) were evaluated in subjects with dementia. The area of the CC and seven distinct subdivisions were measured in subjects with Alzheimer's disease (AD) (n = 162), multi-infarct dementia (MID) (n = 28), and in a healthy comparison group (n = 36). There were significant differences in the regional areas of the CC for both the AD and MID patients relative to values for the comparison subjects. When mildly demented (MMSE > or = 21), subjects with AD had significantly smaller posterior midbody, isthmus, and splenium and subjects with MID had significantly smaller genu relative to comparison subjects. This study reports different patterns of regional CC area loss in subjects with AD and MID.