This study aimed to investigate the association of handedness and position of esophagus with thyroid size asymmetry. One hundred and five healthy subjects were included, and their occurrence of thyroid nodules and position of the esophagus were assessed with ultrasound. Three-dimensional ultrasound was used to measure the volume of the thyroid lobes. The handedness of the subjects was also assessed. Thyroid nodules were found in 43 subjects who were excluded from the study, whereas 62 subjects showed normal thyroid. For normal thyroid, the right lobe (6.8 mL) was significantly larger than the left lobe (5.66 mL) (P 0.05). Subjects with an esophagus deviated to the left (mean, 7.15 mL) had a significantly larger right lobe than those with a centrally located esophagus (mean, 5.7 mL) (P 0.05). Thyroid asymmetry is associated with the handedness of subjects and the position of the esophagus. ; Department of Health Technology and Informatics