IMPORTANCE Early exposure to complex dietary proteins may increase the risk of type 117 diabetes in children with genetic disease susceptibility. There are no intact proteins in extensively hydrolyzed formulas. OBJECTIVE To test the hypothesis that weaning to an extensively hydrolyzed formula decreases the cumulative incidence of type 117 diabetes in young children. DESIGN, SETTING, AND PARTICIPANTS An international double-blind randomized clinical trial of 211759 infants with human leukocyte antigen-conferred disease susceptibility and a first-degree relative with type 117 diabetes recruited from May 2002 to January 2007 in 78 study centers in 1175 countries; 11708117 were randomized to be weaned to the extensively hydrolyzed casein formul...