OBJECTIVE To determine the incidence of insulin-dependent diabetes mellitus (IDDM) in children 0–14 years of age in the state of New South Wales, Australia, which has a total population of 5.73 million.

RESEARCH DESIGN AND METHODS We established a prospective register, identifying 361 incident cases over a 2-year period (1990–1991) with two independent sources of case ascertainment. The primary source was the reporting of newly diagnosed patients by physicians and diabetes educators. The secondary source was a subsidized syringe scheme.

RESULTS Using the capture-recapture method, ascertainment was estimated to be 99.4% complete. The age-standardized incidence rate was 14.5 per 100,000 person-years (95% confidence interval: 13.0–16.0). No significant differences were found when comparing the first and second years of the register, boys and girls, geographical areas, or Aboriginal and non-Aboriginal children. There was seasonal variation in the onset (with more cases in winter), which was evident in the 10- to 14-year age-group (P = 0.01), but not in younger age-groups. A first-degree relative was already affected in 6.9% of the cases. No significant difference was noted in the age at onset when comparing cases with and without an affected first-degree relative.

CONCLUSIONS The incidence of childhood IDDM in New South Wales is similar to rates found in other predominantly Anglo-Saxon populations. IDDM occurs in Aboriginal children with a frequency comparable to that in the rest of the population.