To establish correlations among cognitive states and neuropathology, we have examined 22 subjects (69-97 years of age) from the Baltimore Longitudinal Study of Aging (BLSA), of whom 15 had normal and stable cognitive performances and seven had dementia of variable severity. In the majority of normal subjects, few or no beta-amyloid (A beta) deposits or senile plaques (SP) were present in the neocortex, but neurofibrillary tangles (NFT) were consistently found in CA1 of hippocampus and layer II of entorhinal cortex. In two (15%) normal individuals, the densities of SP were consistent with the diagnosis of possible Alzheimer's disease (AD). We speculate that these cases with normal cognitive states and abundant neocortical SP may represent preclinical AD. We conclude that the neocortex of a majority of cognitively intact individuals can remain free of A beta deposits or SP, even into the tenth decade of life.