The incidence of live-born children with Down syndrome was found to be 1.73/1000 (1:578) in northern Finland over the years 1965 to 1979. Despite a marked reduction in the proportion of older mothers, no significant change in the incidence was observed. Instead, an age-specific rise in the incidence for mothers aged 25 to 29 years could be shown during the last five-year period in years 1975 to 1979.