The Indianapolis-Ibadan Dementia Project, established in 1991, is a longitudinal, prospective population-based comparative epidemiological study of the prevalence and incidence rates and risk factors for Alzheimer's disease and other age associated dementias. The project enrolled community-dwelling elderly (age > 65 years) African Americans living in Indianapolis and Yoruba living in Ibadan, Nigeria, employing the same research design, methods, and investigators.