MRI studies to date have confirmed and expanded upon findings of morphologic differences between the brains of subjects with DS and those of the general population found by CT and post-mortem examination. [table; see text] Hippocam pal and neocortical structures are smaller in DS while unexpectedly the parahippocampal gyrus was found to be larger. MRI has demonstrated that subjects with DS develop signs associated with [table; see text] brain aging at an earlier age. These findings include increased rate of dilatation of ventricles, increased peripheral atrophy, and increased deep white matter lesions. In addition, changes that are associated with AD occur earlier in the DS population. Functional studies reveal decreasing cerebral perfusion with age in adults with DS, a pattern similar to non-DS subjects with clinically progressive dementia, and provide evidence for altered blood-brain barrier permeability. Dynamic MRI studies have also shown adults with DS to have fluctuating cortical CSF volumes, similar to some elderly non-DS subjects and subjects with shunted hydrocephalus. This is a new finding in brain aging that suggests a relationship between aging in DS and edematous states of the brain.