OBJECTIVE— To provide reliable data on the incidence of IDDM in southern Chinese children in Hong Kong. RESEARCH DESIGN AND METHODS— A registry was established in 1991 to collect childhood IDDM cases retrospectively and prospectively from four districts in Hong Kong. The study included all newly diagnosed cases of IDDM with onset < 15 yr of age from 1 January 1986 to 31 December 1990. Primary ascertainment was based on review of medical records at a regional hospital serving the four districts. An independent school survey validated registry data. RESULTS— The completeness of ascertainment was 93.8%. The age-standardized incidence of IDDM was 2.0/100,000/yr with the 95% confidence interval of 1.2–3.0/100,000/yr for children < 15 yr of age during the study period. The incidence rates/100,000/yr for the three age-groups were: < or = 4 yr, 0.8; 5–9 yr, 2.2; 10–14 yr, 2.8. The incidence for males was 1.5/100,000/yr (95% confidence interval 0.7–2.9/100,000/yr) and for females, 2.4/100,000/yr (95% confidence interval 1.3–4.0/100,000/yr). CONCLUSIONS— This study documents a very low incidence rate of childhood IDDM in southern Chinese in Hong Kong.