It is the intent of this study to compare the Age Specific Prevalence and Incidence of dementing disorders, especially Alzheimer's disease in a sample, both community and nursing home dwelling, of Afro-Americans age 65 years and over living in Indianapolis, Indiana (n=2500) and a sample of Nigerians age 65 years and over living in Ibadan (n=2500); to compare the neuropathology of aging and of Alzheimer's disease and other dementing disorders in elderly Nigerian Africans and Indianapolis AfroAmericans; and to conduct a case control and a prospective study of risk factors of Alzheimer's disease in the two communities in association with the World Health Organization multi-centered studies. The WHO has recently initiated a cross national multi-centered etiology oriented study and have selected six sites including Ibadan and Indianapolis to participate in this study. The research design for the prevalence study will follow a two-stage design in which there is an initial screening interview followed by a clinical evaluation on a subset of the subjects who were screened. There will be an interim follow-up of dementia cases and questionable cases one year later, to document course in cases and to determine diagnosis in the questionable cases. The incidence study will be carried out two years after the prevalence study and will replicate the methods of the prevalence study. All subjects who die during the course of the study will be eligible for neuropathological evaluation, for studies of the aging normal brain, and to confirm diagnosis in demented patients. While the evidence accumulates that there is a genetic basis for at least a proportion of patients with DAT, most researchers conclude that environmental risk factors also play a major role in etiology. The establishment of different prevalence and incidence of DAT in different populations would greatly aid the search for these risk factors.