The aim of the study was to investigate whether growth parameters at birth and age 1 year were associated with type 1 diabetes (T1D) in the Danish population and to what extent this explains the increase in T1D incidence. The study is a population-based case-control study; it compares 490 cases from the Danish diabetes register 1996-99 aged 0-14 years and 696 randomly selected controls (2 per case) from the population register matched for gender and date of birth. We found an increased risk of T1D during childhood in children with a body mass index (BMI) on or above two standard deviations at age 1 year (OR = 3.77 [95% CI 1.41, 10.1]). Children developing diabetes were significantly taller at age 1 year (OR = 1.04 [95% CI 1.00, 1.08]). Children born 1981-99 have significantly higher BMI and weight at birth and a significantly lower BMI and weight at age 1 year compared with children born 1966-74. Thus the increasing incidence of T1D could not be explained by changes in growth parameters at birth or at age 1 year.