This study aimed to determine the rate of progression to diabetes after seroconversion to islet autoantibodies in children at risk for type 1 diabetes. Data from three prospective cohort studies in Colorado, Finland, and Germany were pooled to analyze the development of insulin autoantibodies, glutamic acid decarboxylase 65 (GAD65) autoantibodies, insulinoma antigen 2 (IA2) autoantibodies, and diabetes. The primary analysis focused on children with multiple islet autoantibodies, while a secondary analysis included children with a single autoantibody or no autoantibodies. Key findings include: - 585 children with multiple islet autoantibodies had a 69.7% risk of progressing to diabetes within 10 years, compared to 14.5% for those with a single autoantibody. - The risk was significantly higher in children with multiple autoantibodies (79.1% at 15 years) compared to those with no autoantibodies (0.4%). - Progression was faster in children who seroconverted before age 3 years, had the HLA genotype *DR3/DR4-DQ8*, or were female. - The study highlights the need for interventions to prevent or delay the development of multiple islet autoantibodies and progression to type 1 diabetes.This study aimed to determine the rate of progression to diabetes after seroconversion to islet autoantibodies in children at risk for type 1 diabetes. Data from three prospective cohort studies in Colorado, Finland, and Germany were pooled to analyze the development of insulin autoantibodies, glutamic acid decarboxylase 65 (GAD65) autoantibodies, insulinoma antigen 2 (IA2) autoantibodies, and diabetes. The primary analysis focused on children with multiple islet autoantibodies, while a secondary analysis included children with a single autoantibody or no autoantibodies. Key findings include: - 585 children with multiple islet autoantibodies had a 69.7% risk of progressing to diabetes within 10 years, compared to 14.5% for those with a single autoantibody. - The risk was significantly higher in children with multiple autoantibodies (79.1% at 15 years) compared to those with no autoantibodies (0.4%). - Progression was faster in children who seroconverted before age 3 years, had the HLA genotype *DR3/DR4-DQ8*, or were female. - The study highlights the need for interventions to prevent or delay the development of multiple islet autoantibodies and progression to type 1 diabetes.