¹¹C-Pittsburgh compound B (PiB) uptake in PET images is frequently used to analyze β amyloid (Aβ) deposition in living individuals, but its correlation with histologically determined Aβ has not been examined. Six individuals with dementia underwent PiB-PET imaging, and their brains were analyzed neuropathologically (mean interval between imaging and death: 816 days; PiB positive:negative, 3:3; male:female, 3:3; mean age: 84.0 years). PiB uptake (reported as standardized uptake value ratio [SUVR]) was analyzed in 11 cortical regions and 10 subcortical grey matter areas and compared with the Aβ load (% area [the percentage of total area positive for Aβ] and number of neuritic plaques) seen with immunohistochemical staining with an anti-Aβ 11-28 antibody. Two PiB-positive subjects had abundant neuritic plaques and were diagnosed with Alzheimer’s disease (AD). SUVR and % area were strongly correlated in the cortical regions of these subjects (subject 1: r = 0.65, p = 0.03; subject 2: r = 0.80, p = 0.003). The other PiBpositive subject (subject 3) showed focal PiB uptake. In subject 3 and the 3 PiB-negative subjects (subjects 4-6), there was no correlation between regional SUVR and % area or neuritic plaques. PiB uptake was not correlated with Aβ deposition in subcortical regions. High PiB positivity in the cerebral cortex suggests the presence of substantial Aβ deposition and neuritic plaques associated with the pathologic changes of AD. Our results suggest that high cortical SUVR is a reliable marker of AD. Subcortical PiB positivity must be interpreted more carefully.