The relationship between type 1 diabetes mellitus (T1DM) and autoimmune thyropathies is well known and has been described in the literature. Based on present knowledge, the relationship between thyropathies and other forms of diabetes, such as monogenic diabetes, has not been investigated. The aim of our study was to assess the prevalence of autoimmune thyroid diseases (ATD) in children and adolescents with maturity onset diabetes of the young type 2 (MODY2) in comparison with patients with T1DM and a control group.We examined 23 children and adolescents with MODY2 (11 F/12 M; 13.5 ± 5.3 years) and 166 patients with T1DM (80 F/86 M; 14.0 ± 4.7 years). The control group consisted of 62 age-matched healthy subjects (34 F/28 M). ATD diagnosis was based on the finding of one or more positive thyroid autoantibodies and characteristic thyroid ultrasound lacking homogeneity, with a hypogenic or mixed echo pattern.ATD was diagnosed in 15 (10.5%; 9 F/6 M) patients with T1DM, in 4 with MODY2 (17.4%; 4 F), and in 1 (1.6%) control. A significantly higher ATD prevalence was detected in T1DM and MODY2 compared to the control subjects (p = 0.02), without differences between T1DM and MODY2 (p = 0.26). There were no gender differences noted in T1DM (p = 0.42); on the contrary, in MODY2 a higher prevalence was noted in females (p = 0.04). Celiac disease and a positive family history of ATD were not detected in subjects with MODY2.Our study showed an increased prevalence of ATD in patients with MODY2. Therefore, a careful follow-up of all children with MODY2 is recommended in order to assess the presence of thyroid disorders.