Lewy bodies (LBs)are found throughout the brain stem, limbic and neocortical areas in Parkinson's disease. Lewy bodies are also associated in these areas with dementia and the substrate of 'dementia with Lewy bodies' is thought to include Lewy body pathology in limbic and neocortical areas with or without Alzheimer-type changes. In order to determine whether dementia with Lewy bodies is characterised primarily by cortical or limbic LB pathology, we have measured the density of Lewy bodies, neuritic plaques and neurofibrillary tangles in 12 neocortical, limbic and brain stem sites in 10 patients who were pathologically diagnosed with diffuse Lewy body disease (DLBD) (64.7 +/- 2.7 years). The mean LB density in limbic areas (3.00 +/- 0.61/mm2) was significantly greater than that of neocortical areas (1.13 +/- 0.22/mm2, P < 0.001). The greatest density of LBs was found in the amygdala (4.1 +/- 0.7/mm2) and the lowest in the occipital cortex (0.3 +/- 0.1/mm2). In limbic areas, LB formation positively correlated with neuritic plaque formation (r = 0.51, P < 0.01) but not with neurofibrillary tangle densities. These data indicate that dementia with Lewy bodies is characterised primarily by limbic, and secondly by neocortical, LB pathology. It remains to be determined why limbic areas are selectively vulnerable to LB pathology in dementia with Lewy bodies.