Standardized childhood insulin-dependent diabetes mellitus (IDDM) incidence data were collected from 21 ethnic groups in 10 countries to evaluate temporal trends in the disease between 1966 and 1986. Population-based registries contributed information concerning periods from 6 to 21 yr. The incidence rates were modeled with Poisson regression. For the past 2 decades, a linear increase in IDDM risk for people <15 yr of age has been observed in most of Europe and the Western Pacific but not in North America. The temporal variation did not appear to differ significantly by age or sex in most locations. The observed pattern of temporal variation suggests that a proportion of diabetes in childhood may be caused by a potentially preventable environmental factor.