Objective— To report the incidence of IDDM in the age-group 0–29 yr in the Province of Turin, Italy (951, 445 inhabitants 0–29 yr of age), over a 5-yr period (1984–1988) according to age, sex, and geographical region within the area and to identify any temporal trend. Research Design and Methods— The survey used as the primary data source the list of all patients attending diabetic clinics, and as secondary data source, used the list of hospital discharges for diabetes. Results— We identified 298 incident cases of IDDM in people 0–29 yr of age. Estimated completeness of ascertainment of the registry was 97%. Age-adjusted (world-standard) incidence rates were 7.40/100,000 (95% CI 6.28–8.71), 5.83 (4.95–6.86), and 6.70 (5.97–7.51), respectively, in the age-groups 0–14, 15–29, and 0–29 yr. Incidence was significantly higher in males than in females in the age-group 15–29 yr (7.36, 6.02–8.98, vs. 4.21, 3.12–5.56). An increasing incidence from rural areas to the greater Turin area (city and its industrial belt) was evident. No significant temporal trend during the study period was found, although year-to-year variability was evident, with the highest incidence in 1984. Conclusions— This study suggests a high male-to-female ratio of incidence of IDDM after 14 yr; either sex hormones or different exposure to environmental determinants could be involved.