This study was performed to investigate whether the body mass index (BMI) of diabetic children at manifestation is related to the non-random risk distribution in Austria and whether there is an association with the BMI of the background population. All newly diagnosed cases aged <15 years (n=1644) from 1989 to 2000 were allocated to districts using the postal code. BMI at the time of diagnosis was derived from the Austrian incidence data sheet in 99.3% of the registered cases. Data on BMI of the whole population >14 years of age for the year 1991 and birth weight for the years 1989-1999 were derived from Statistics Austria. Linear regression as well as ecological regression (Poisson) models with correction for non-linearity were used. BMI at diabetes manifestation was positively associated with year of diagnosis (P<0.05) and the age at diagnosis (P<0.01). An increase in BMI when moving from West to East (P<0.01) and a higher BMI at diagnosis in boys than girls (P<0.01) was observed. The ecological regression model showed a positive significant association of BMI in newborns and a positive trend of BMI in the background population with incidence rates. Conclusion: our data support the hypothesis that obesity may be a risk factor not only for type 2 but for type 1 in children acting as an accelerator for the clinical manifestation.