The purpose of this study was to establish a "normal" range of dimensions of the thyroid gland on routine neck computed tomography in the Korean population and to investigate the possible influence of some physiological factors on the thyroid dimension. Neck computed tomography scans of 100 adults (57 males, 43 females; mean age=55.2 years) were reviewed retrospectively to measure the size of the thyroid gland and to evaluate its relationship to the trachea and cervical vertebra. For right and left lobes, the mean width was 15.7+/-2.6 mm and 15.2+/-3.1 mm, the mean thickness was 20.9+/-3.4 mm and 18.9+/-3.4 mm, the mean length was 61.8+/-8.6 mm and 58.5+/-8.3 mm, the mean estimated volume of each lobe was 8.8+/-3.1 cm(3) and 7.6+/-3.0 cm(3), respectively. The mean volume of total thyroid glands (including isthmus) was 17.5+/-6.6 cm(3). There was no significant difference between the total study group and the normal thyroid function group. The dimensions of the right lobe were significantly larger that those of the left. There was no significant difference between males and females. In multiple regression analysis, it was likely that the influence of body weight on the thyroid dimension was most pronounced. Our study presents initial data for assessing the thyroid gland on neck computed tomography scans in Koreans, and thereby provides suitable limit values of normal thyroid glands.