The incidence of insulin-dependent diabetes mellitus (IDDM) in Denmark in the years 1970--1976 was 13.3 per 100,000 in the age group 0--29 yr. This incidence is almost identical to that found in 1924 in Denmark in the same age group. The prevalence of insulin-consumers is 3.2 per 1,000. Comparison is made with incidence and prevalence data from other studies of Caucasian populations.