The nucleus basalis of Meynert (nbM), a cholinergic nuclear group located in the sublenticular region, receives afferent input principally from the limbic system and projects to most of the cerebral cortex. The nucleus is atrophic in dementia of the Alzheimer type (DAT) and several other dementing disorders and attempts have been made to relate cholinergic deficits as well as intellectual impairment to nbM alterations. A cortical cholinergic deficit is routinely associated with atrophy of nbM, but there is no consistent relationship between changes in nbM and histopathologic alterations of the Alzheimer type and a variable association between nbM changes and dementia. The available information suggests that atrophy of nbM and cortical cholinergic deficits have a contributory role in several dementia syndromes but cannot account for many pathologic and behavioral aspects of these disorders.