Objective: This study aimed to assess the iodine deficiency, prevalence of goitre among schoolchildren and measuring environmental iodine in Taif city, Saudi Arabia. Methods: A cross-sectional multistage cluster-sampling methodology was done on 1887 schoolchildren. Their urinary iodine concentration (UIC) and goitre prevalence was assessed. Blood level of triiodothyronin, thyroxine and thyroid-stimulating-hormone was carried out for students with normal, mild; moderate and sever iodine deficiency. The iodine content of salt, water and soil was also assessed. Results: Goitre prevalence was 7.4% and about 71% of the participants had UIC less than 100μg/L. An inverse relationship between median UIC and the percent prevalence of goitre was found. The mean serum T3, T4 and TSH were 1.05ng/dL, 6.81μg/dL, and 5.69mIU/L, respectively. A significant positive correlation was found between the mean value of urinary iodine and the mean value of both T3 and T4. While a significant negative correlation between the mean value of urinary iodine and the mean value of TSH was also noted. Conclusions: The results revealed the presence of a potential public health problem of iodine deficiency among school going children in high altitude areas of Saudi Arabia. There is a need to monitor and evaluate the salt iodization process, and distribute adequately iodized salt in the affected areas.