CONTEXT: Rapid growth has been suggested to promote islet autoimmunity and progression to type 1 diabetes. Childhood growth has not been analyzed separately from infant growth period in most previous studies, which may have distinct features due to differences between those stages of development. OBJECTIVE: We aimed to analyze the association of childhood growth between 1-8 years of age with development of islet autoimmunity and progression to diagnosis of type 1 diabetes. DESIGN: Longitudinal data of childhood growth between 1-8 years of age and development of islet autoimmunity and type 1 diabetes was analyzed in a prospective cohort study. PARTICIPANTS: 10,145 children from Finland, Germany, Sweden, and the United States, 1.0-8.0 years of age with at least three height and weight measurements and at least one measurement of islet autoantibodies. OUTCOMES: Appearance of islet autoimmunity and progression from islet autoimmunity to type 1 diabetes between 1-8 years of age. RESULTS: Rapid increase in height (cm/year) was associated with increased risk of seroconversion to glutamic acid decarboxylase autoantibody, insulin autoantibody or insulinoma-like antigen-2 autoantibody (HR=1.26 (95%CI=1.05, 1.51) for 1-3 years of age and HR=1.48 (95%CI=1.28, 1.73) for >3 years of age). Furthermore, height rate was positively associated with development of type 1 diabetes (HR=1.80 (95%CI=1.15, 2.81)) in the analyses from seroconversion with insulin autoantibody to diabetes. CONCLUSIONS: Rapid height growth rate in childhood is associated with increased risk of islet autoimmunity and progression to type 1 diabetes. Further work is needed to investigate the biological mechanism that may explain this association.