The article highlights new data on the effect of thyroid dysfunction on the formation of secondary amenorrhea in adolescent girls who live for a long time in conditions of weak iodine deficiency. The objective: to determine the state of the thyroid system in girls with SA, taking into account the presence of thyroid disorders. Materials and methods. Under observation were 68 girls aged 14-17 years with SA, living in conditions of weak iodine deficiency in Kharkov and the Kharkov region. The examination provided for an ultrasound of the thyroid gland and determination of the functional state of the pituitary-thyroid system. Girls with SA entered the main group. Depending on the presence of thyreopathy, namely, diffuse non-toxic goiter (DNG), the patients of the main group were divided into two subgroups: 1-st subgroup consists of a girls with SA and normal thyroid volume (n=39); 2-nd subgroup consists of girls with SA and DNG (n=29). The control group included 78 female peers with normal thyroid volume, harmonious physical development and normal menstrual function. Results. The obtained results allowed to establish that the formation of SA in girls living in conditions of low iodine deficiency occurs against a background of thyroid dysfunction, the character of which differs in girls with normal thyroid gland volume and DNG. This can be regarded as a succession of stages of the pathological process when, in conditions of prolonged residence in regions with a mild iodine deficiency, a distearosis is formed which is characterized by an increase in the fT4 conversion in fT3, reflecting an increase in the fT3/fT4 ratio in the vast majority of the girls surveyed. These changes in the thyroid profile negatively affect the development of the reproductive system and can cause menstrual dysfunction even in the absence of thyroid disease. The conclusion. Prevention and treatment of SA in girls living in conditions of low iodine deficiency, provides long-term use of pharmacological drugs potassium iodide in age doses. Key words: girls, thyroid gland, thyroid status, secondary amenorrhea.