Our aim was to investigate the occurrence of clinical and subclinical autoimmune thyroid disease in 79 patients with celiac disease as reflected in thyroid function, antibodies, and ultrasound. Since subclinical thyroid diseases are common in the population, 184 nonceliac controls were also studied. Normal thyroid function combined with positive antibodies and marked hypoechogenicity was considered subclinical disease. Autoimmune thyroid disease was observed in 13.9% of celiac patients and in 2.1% of controls (P = 0.0005); and subclinical disease in 10.1% and 3.3%, respectively (P = 0.048). The mean thyroid gland volume was 8.3 ml in celiac patients and 10.4 ml in controls (P = 0.007). Hypoechogenicity was found in 73% of celiac patients and in 42% of controls (P < 0.0001). Positive thyroid antibodies were associated with hypoechogenicity in celiac patients but not in controls. In conclusion, the occurrence of both clinical and subclinical autoimmune thyroid disease was increased in celiac disease; subclinical thyroid disease indicates regular surveillance.