Background: Iron deficiency is the most common single-nutrient deficiency disease in the world and is a major concern for about 15% of the world population. It has been shown that iron deficiency may affect thyroid hormones. Objective: To determine thyroid hormone status in iron deficient adolescent girls. Methods: A cross-sectional study was carried out in Lar Province and its’ vicinity in South of Iran. By a stepwise random sampling from all public girls’ high schools in Lar and its’ vicinity, using World Health Organization (WHO) criteria, 94 iron deficient subjects were selected. Urine and serum samples were collected and assayed for urinary iodine and serum ferritin, iron, TIBC, TSH, T4, T3, FT4, FT3, T3RU, rT3, selenium and albumin concentrations. Results: Hematological indices for iron status confirmed that all of subjects were iron deficient. There was a positive correlation between plasma T4 and serum ferritin (p<0.001). Subjects with low serum ferritin had a higher T3/T4 ratio (p<0.001). Using a stepwise regression analysis, it was found that among the variables studied, only ferritin contributed significantly to rT3 concentration (p<0.004). Conclusion: Iron deficiency may impair thyroid hormone status in iron deficient adolescent girls.