The prevalence of dementia is changing over time in Rochester, Minnesota.

Resources of the Rochester Epidemiology Project were used to estimate prevalence rates for dementia on January 1, 1975, 1980, and 1985, and to evaluate trends over time. Prevalence rates increased with age for both men and women. There was no difference in the prevalence rates for January 1, 1975, and January 1, 1980, but there was a significant increase between January 1, 1980, and January 1, 1985. Similar results were found for Alzheimer's disease. Age was an important factor in the trend data. The apparent increase in prevalence over time is probably multifactorial.