An 82-year-old cognitively healthy man was assessed longitudinally until very mild senile dementia of the Alzheimer type was diagnosed by clinical research criteria and documented by psychometric testing at age 85 years. Four months after diagnosis, Alzheimer's disease was confirmed neuropathologically. The diagnostic difficulties involved in distinguishing early senile dementia of the Alzheimer type-Alzheimer's disease from normal aging are examined and clinical and pathologic features useful for their discrimination are discussed.