Background & Objectives: Goiter prevalence in school age children is an indicator of the severity of iodine deficiency disorders (IDD_S) in the society and a goiter prevalence ≥5 % in school age children indicates a public health problem. In area of mild to moderate IDD_S, measurement of thyroid volume by ultrasonography through observation is preferrable to population for grading goiter. Considering the importace of this issue, because of being mountainous and lack of this method's application for determining the incidence of goiter this study was desinged.

 Methods: In this descriptive – analytical study, thyroid volumes of 230 boys between 12 to 15 years old were measured by portable ultrasonograph in Tabriz. Also urinary iodine concentrations were determined by method A (Sandell-kolthoff reaction).

 Results: Mean of subjects’ thyroid volume was 8.12 ±2.21 ml and with latest references of Iran and WHO/NHD, goiter prevalence was taken based age 51.7 % and based surface body 81.1 %. Urinary iodine median of tested samples was 15.2µg/dl and iodine deficiency prevalence was 29.1 % . There was no significant correlation between urinary iodine and thyroid volume.

 Conclusion: Large thyroid volume of middle school boys in Tabriz is probably due to iodine intake deficiency in the first years of their life. Also, the role of goitrogenic factors and effect of climate condition on thyroid volume and goiter prevalence of middle school boys in Tabriz shouldn't be ignored. Further studies are recommended for determination of a local reference for thyroid volume Also it is necessary to be sure from consumption of iodine salt and its standardization.