To the Editor: The risk of type 1 diabetes among the monozygotic twins of patients with type 1 diabetes is reported to be as low as 30%; this percentage is usually based on the ascertainment of data at a single time point.¹–³ Less is known about the cumulative incidence of islet antibodies and diabetes among twins followed over time.⁴,⁵ We analyzed the long-term risk of islet autoimmunity and type 1 diabetes in a cohort of twins of patients with type 1A diabetes as defined by the American Diabetes Association criteria (95% of the twins with a prediabetic condition . . .