Type 1 diabetic children and adolescents often present with autoimmune thyroid disorders. Two hundred and four diabetic patients, less than 20 years old, were studied in order to diagnose these diseases. The prevalence of thyroid autoimmune disorders was 17.6% and, of those, chronic autoimmune thyroiditis was the most frequent. Microsomal autoantibodies correlated more accurately with the presence of chronic autoimmune thyroiditis than thyroglobulin autoantibodies. The thyroid status of most of the patients with positive markers was euthyroidism (77%), but subclinical hypothyroidism (11%), overt hypothyroidism (3%), subclinical hyperthyroidism (3%) and overt hyperthyroidism (6%) were also present. Autoimmune thyroid disorders were the most prevalent immunological processes affecting diabetic patients. No significant associations of thyroid autoimmunity and other autoimmunological disorders, such as celiac disease or presence of other autoimmune antibodies, were found.