Data from a 1973 survey of diabetes mellitus among schoolchildren in Michigan have been analyzed to derive age-specific incidence and prevalence rates. The annual incidence of new cases of diabetes is approximately 20/100,000 children from age four through age 17, with the highest incidence rates at age nine through age 12. The prevalence rates to be expected, if the most recent incidence rates persist, are approximately 50/100,000 at age five, 150/100,000 at age ten, 270/100,000 at age 15, and 325/100,000 by age 18. The incidence rate of diabetes in Michigan children appears to have doubled between 1959 and 1972. Data from Erie County, New York, suggest that this secular trend has been evident since 1949, and data from Norway suggest that the trend could be noted 50 to 70 years ago.