Objective To report the incidence of type Ⅰ diabetes mellitus (IDDM) of children in Shijiazhuang. Methods A retrospective study was carried out in children (aged 0～14 years) with IDDM at onset in Shijiazhuang during 1985～1997. Cases were collected from hospitals (primary source), primary schools, middle schools, and kindergartens (secon d source). Results We found 51 children (23 boys, 28 girls) wit h type I diabetes mellitus. The average crude annual incidence rate was 0.60 per 100 000 (95% CI: 0.44～0.77), adjusted annual incidence rate was 0.64 per 100 000 (95% CI: 0.35～0.93) and ascertainment corrected incidenc e rate was 0.71 per 100 000 (95% CI: 0.53～0.88). In 1985 there was a incidence peak, and the incidence was particularly high in spring and autumn . The incidence rate was higher in the 10～14-year group than in other groups (0 ～4-year group and 5～9-year group) and the peak incidence fell at 4 years and 1 4 years. There was no significant difference in boys and girls. Conclusi ons The onset of IDDM in children appears to be relative to children's age and the specific season.