Background: In Finland, the incidence of insulin-dependent diabetes mellitus (IDDM) in children aged < 15 years is the highest in the world. The aim of this study was to determine the temporal variation in incidence and the age distribution at diagnosis of IDDM.
Subjects and methods: Data on incidence of IDDM in Finland nationwide were obtained from two sources: the Central Drug Registry for the years 1965-1986 (6195 IDDM cases) and the prospective IDDM registry for the years 1987-1992 (2062 IDDM cases). The annual incidence rates were calculated per 100,000 population. The increase in incidence from 1965 to 1992 was estimated by fitting the linear regression with the annual incidence data.
Results: The overall incidence of IDDM between 1987 and 1992 was 36 per 100,000/year. During 1965-1992 the increase was almost linear. The regression-based change in incidence was 2.8% per year. In the 1970s the increase in incidence was steepest in 5-9 year olds and since the mid-1980s in those < 5 years old at diagnosis.
Conclusions: The incidence of IDDM in Finnish children seems to increase further. During the last decades the increase in incidence has been almost linear with occasional peaks. The age-at-diagnosis of IDDM has been moving towards the younger ages, and differences in incidence between age groups have now almost disappeared among Finnish children aged 1-14 years.