The distribution and density of diffuse, primitive and classic beta-amyloid (A beta) deposits in the medial temporal lobe (MTL) was studied in cases of dementia with Lewy bodies (DLB) with and without associated Alzheimer's disease (AD) and 15 cases of sporadic AD. In the 'pure' DLB cases, virtually no A beta deposits were observed in the CA regions of the hippocampus or dentate gyrus whereas deposits were distributed throughout the MTL in DLB/AD and AD cases. Densities of diffuse and primitive A beta deposits were similar in AD and DLB/AD cases but density was significantly reduced in the 'pure' DLB cases. The density of the classic deposits was significantly reduced in DLB cases with or without associated AD compared with AD cases. These results suggest that A beta deposition in the MTL in 'pure' DLB cases is similar to that of elderly non-demented patients while, with the exception of the classic deposits, A beta deposition in DLB/AD cases is similar to that in cases of AD alone.