Objective:The aim of this study was to investigate in patients with type 1 diabetes (T1D):the prevalence of thyroid autoantibodies (T-Ab);the association between thyroid autoimmunity with either islet autoantibodies or thyroid function;and the differences of thyroid autoimmunity between adults and pediatrics. Methods:A total of 491 T1D patients were analyzed for thyroid autoimmunity in addition to islet autoantibodies and thyroid function. Results:Tweenty-two percentage T1D patients had thyroid autoantibodies (62% were female). Patients with T-Ab had higher prevalence of islet autoantibodies (all P <0.05). While thyroid peroxidase (TPOAb) was positively associated with all the 5 islet autoantibodies (all P < 0.05),thyroglobulin (TGAb) was only associated with glutamic acid decarboxylase antibody (GADA,P=0.005). In addition,the positive number of islet autoantibodies was positively associated with the prevalence of T-Ab (30.2%,P=0.000). Tweenty-two point six percentage adults with T1D had T-Ab,adults with double anti-thyroid autoantibodies positivity was more than that in the pediatric group (prevalence of double T-Abs:57.8% vs 36.4%,P=0.028). The presence of T-Ab was positively associated with serum thyroid-stimulating hormone (TSH) levels (P=0.008). The presence of both anti-thyroid antibodies was positively associated with thyroid dysfunction (prevalence of thyroid dysfunction:64.2% vs 30.9%,P=0.002). Conclusion:Thyroid autoimmunity was commonly happened in adults and pediatrics with T1D. Thyroid autoimmunity was associated with female gender,the persistence of GADA and multiple islet autoantibodies positivity. The risk of thyroid autoimmunity did not differ from adults to pediatrics;however,the thyroid autoimmunity was severe in the adults. Multiple anti-thyroid autoantibodies indicated thyroid dysfunction.