Trends in incidence of dementing illness in Rochester, Minnesota, in three quinquennial periods, 1960-1974.

We ascertained the incidence of dementias of all causes between 1960 and 1975 among citizens of Rochester, Minnesota. Study of all medical records yielded incidence rates for the quinquennial periods of 1960-1964, 1965-1969, and 1970-1974. In the population at risk (30 years or older), the age-adjusted rates (per 100,000 population/year) for Alzheimer's disease (clinically diagnosed or pathologically confirmed, or both) in the three periods were: 104.9, 80.8, and 96.6. The rates for dementia of all causes were: 160.6, 122.0, and 136.8. Calculation of 95% confidence intervals showed that the incidence rate for dementia or Alzheimer's disease has not changed in this 15-year period in Rochester, Minnesota. Assuming no demented patients younger than 29 years, the incidence rates in the three quinquennial periods for all dements were 79.4, 60.3, and 67.7; for Alzheimer's disease they were 51.9, 40.0, and 47.8.