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.