The hypothesis for this study is that weaning to an extensively hydrolyzed infant formula will decrease the incidence of type 1 diabetes (T1D), as it does in all relevant animal models for the disease. This will be tested in children who carry risk-associated human leukocyte antigen genotypes and have a first-degree relative with T1D. The trial will use a double-blind, prospective, placebo-controlled intervention protocol, comparing casein hydrolysate with a conventional cow's milk (CM)-based formula. A secondary aim is to determine relationships between CM antibodies, a measure of CM exposure, and diabetes-associated autoantibodies. To achieve an 80% power for the detection of a 40% intervention-induced difference in the development of autoantibodies and subsequent diabetes, the study requires 2032 subjects. A multicenter, international, collaborative effort is necessary to achieve recruitment targets. A collaborative international study group of 78 clinical centers in 15 countries has therefore been assembled for this purpose.