The pathologic substrate of the clinical syndrome of dementia with Lewy bodies (DLB) remains to be determined. Only a few prospective clinicopathologic studies have been reported. In those reports, most cases of DLB had neocortical or limbic Lewy bodies and Alzheimer-type pathology below threshold for diagnosis of Alzheimer's disease. These results are in accord with recent retrospective clinicopathologic studies of dementia occurring in Parkinson's disease, in which cortical Lewy bodies, rather than concurrent Alzheimer's disease, are increasingly recognized as the pathologic substrate of dementia. Additional clinicopathologic studies are warranted to address the role of other Lewy-related pathology, most notably Lewy neurites, in the cognitive impairment of DLB.