Is the prevalence of dementia changing?

We compared the point prevalence rates of dementing illnesses in the population of Rochester, Minnesota, on January 1, 1980, with the previously published rates of January 1, 1975, by using extensive health care records available from all sources of care in the community, in order to identify and classify cases with standard diagnostic criteria derived from DSM-III. The overall age- and sex-adjusted prevalence rate per 100,000 population for dementia on January 1, 1980, was 402.5 compared with 388.4 on January 1, 1975; for Alzheimer's disease it was 259.8 in 1980 and 259.5 in 1975. The stability of the rates suggests no change in the incidence and mortality associated with these conditions. The prevalence rates for Rochester, Minnesota, are similar to many other rates estimated in other North American communities, but they differ from two other population-based estimates from East Boston and California. Case definitions and methods of assessment probably account for the differences in estimated prevalence.