Two subtypes of Alzheimer's disease (AD) have been commonly identified: early- and late-onset forms. Previous studies suggest that early-onset AD patients have more neuritic plaques (NPs) and neurofibrillary tangles (NFTs). In the current study, NP and NFT counts were performed for 8 brain regions in 25 subjects with definite AD. A repeated-measures analysis of variance of mean regional NP and NFT counts for early- and late-onset groups was performed. A significant between-subject effect indicating greater overall NP and NFT burden in the early-onset group was observed (NP: F = 6.8, df = 1, P = .015; NFT: F = 7.5, df = 1, P = .012). This analysis supports the hypothesis that early-onset AD is associated with greater pathologic burden than late-onset AD. This suggests that late-onset AD patients have less cognitive reserve than early-onset patients and require fewer pathologic changes to exhibit cognitive deterioration.