Background:Celiac disease (CD) may be associated with other immunologic disorders in adults and children. Previous studies linking CD and autoimmune thyroid disease in children have included very few patients with limited biochemical and immunologic screening tests. The aim of this multicenter study was to establish the prevalence of autoimmune thyroid involvement in a large series of pediatric patients with CD.Methods:Five hundred seventy‐three consecutive pediatric patients were enrolled from clinics in Torino, Bologna, Foggia, Rome (two clinics), Naples, and Bari. Three hundred forty‐three patients with CD were studied, 230 girls and 113 boys (median age, 8.5 years). Two hundred fifty‐six of the patients with CD (median age, 9 years) had been following a gluten‐free diet for 3 months to 16 years; 87 patients were untreated (median age, 6.2 years). The diagnosis of CD was made using the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) criteria. A control group of 230 subjects (median age, 8.3 years) was enrolled. Serum free triiodothyronine, free thyroxine, and thyroid‐stimulating hormone (TSH), antithyroperoxidase, antithyroglobulin, anti‐TSH receptor antibodies, and thyroid echographic pattern were considered.Results:Autoimmune thyroid disease was found in 90 of 343 (26.2%) patients with CD (62 on a gluten‐free diet) and in 20 (10%) of the control subjects (P= 0.001). Fifty‐four (15.7%) patients with CD and autoimmune markers had normal thyroid function (euthyroidism) as did 12 (6.0%) of the control subjects; hypothyroidism was observed in 28 (8.1%) patients with CD and in 7 (3.5%) of the control subjects. Hyperthyroidism was diagnosed in four patients with CD and in none of the control subjects with autoimmune markers. An abnormal echographic pattern was seen in 37 patients with CD (16.8%) and only in 1 (1.6%) of the control subjects (P= 0.002).Conclusions:The high frequency of autoimmune thyroid disease found among patients with CD, even those on a gluten‐free diet, may justify a thyroid status assessment at diagnosis and at follow‐up evaluation of children with CD.JPGN 37:63‐66, 2003.