To determine the functional state of the pituitary-thyroid system in conditions of iron deficiency in 371 girls aged 12-17 years was examined. The data of clinical blood tests, biochemical indices of iron metabolism, urinary iodine excretion, thyroid structure, and function are presented. Analysis of the seven-years observation in adolescent girls revealed a significant prevalence of iron deficiency conditions and euthyroid goiter. The iron deficiency in girls was found to increase the risk for euthyroid goiter formation by 10 times. Significant correlations were determined between thyroid volume indices, levels of thyroid-stimulating hormone (TSH), free thyroxine (cT4), the titer of antibodies to thyroid peroxidase (A-TPO) in blood plasma, changes in hemogram and iron metabolism. Violations of thyroid status and iron metabolism are subclinical manifestations of latent iron deficiency in adolescent girls, which are a risk group for the development of iron deficiency conditions. Iron deficiency has been proven to be a significant risk factor for the formation of euthyroid goiter in girls. In iron deficiency conditions in adolescent girls, structural and functional disorders of the thyroid gland should be excluded and its damage should be prevented.