Objective: The frequency of thyroid autoantibodies in autoimmune thyroid disease is known to vary between countries. We aimed to determine the frequency of autoantibody positivity and the correla tion between sonographic findings and autoantibodies in autoimmune thyroid disease. Methods: Laboratory findings and ultrasound findings of 490 patients with Hashimoto’s thyroiditis and 225 patients with Graves’ disease were retrospectively enrolled from a tertiary center. Results: Anti-thyroid peroxidase and anti-thyroglobulin positivity were 90.2% and 60.2% in Hashimoto’s thyroiditis patients, respectively. Anti-thyroglobulin titers were significantly higher in males (P < .01). Mean thyroid volume of Hashimoto’s thyroiditis patients was 10.5 ± 6.9 mL and 11.6% of patients had atrophic thyroiditis (<4 mL). Correlation analysis proved a positive correlation between anti-thyroid peroxidase titers, parenchymal heterogeneity (determined as mild, moderate, and severely heterogeneous) and a weak positive correlation with the thyroid volume and increasing heterogeneity (P < .001, P < .001, r=0.273,) respectively. TSH receptor antibody, anti-thyroid per oxidase, and anti-thyroglobulin positivity were found to be 84%, 75.1%, and 48.4%, respectively, in Graves’ disease patients. The mean thyroid volume of the Graves’ disease group was 22.2 ± 13.9 mL. When the patients were grouped according to their TSH receptor antibody levels (i.e., >30 U/L, 10-30 U/L, <10 U/L) and parenchymal heterogeneity, severe heterogeneity in the group with TSH receptor antibody >30 U/L was found to be significantly higher than the others (P=.049). Conclusion: In conclusion, the most prevalent antibody detected in Hashimoto’s and Graves’ disease is anti-thyroid peroxidase and TSH receptor antibody, respectively, in Turkish patients. Furthermore, a significant relation was found between anti-thyroid peroxidase positivity and anti-thyroid peroxidase titer and the degree of sonographic heterogeneity.