Patients with type 1 diabetes (T1D) are more likely to develop other autoimmune diseases than the general population.

To describe additional autoimmunity in a cohort of children and adolescents with T1D, as well as to identify factors associated with the presence of additional autoantibodies (AABs) and of additional autoimmune diseases (AADs).

This was a single-center retrospective cohort study of 179 children and adolescents (median age: 9.1 years) diagnosed with T1D between 2014 and 2020 in a specialized center in France. Patients were screened for autoimmune thyroiditis and celiac disease at T1D diagnosis and once every 1–2 years during follow-up. Other AADs and their specific autoantibodies were screened for only if clinical or laboratory signs were present.

At T1D diagnosis, 15.6% of participants presented with at least one type of AAB including antibodies specific to Hashimoto's disease (TPOAb and/or TGAb) and/or to celiac disease (tTGAb and/or EMAb). Only 2.8% of participants presented with an AAD as early as T1D diagnosis. The median follow-up was 37 months. The cumulative incidence of AABs and AADs at 2 years of follow-up was, respectively, 3.9% and 5.4%, and it doubled at 3 years of follow-up. Only one patient, also affected by Down syndrome, was diagnosed with 2 AADs. Hashimoto's disease was the most frequently diagnosed AAD, followed by celiac disease, both at an asymptomatic stage. Vitiligo and Graves’ disease were also diagnosed in this cohort but affected few patients. Children aged 6–12 years were more likely to present with an AAD at diabetes diagnosis (p = 0.043).

: The high prevalence and incidence of additional autoimmunity in children and adolescents with T1D justifies regular screening of AABs and AADs.