Among the novelties of our study are the association of thyroid autoimmunity with the presence of anti-GAD, the effect of age at diabetes diagnosis and diabetes duration on the development of thyroid autoimmunity, the long-term follow-up of the patients and the progress from thyroid antibody positivity to subclinical and clinical hypothyroidism, and also the effect of subclinical hypothyroidism on the children’s growth. This evidence concerns the gene GAD1 and diabetes mellitus.