A clinical and epidemiological study including 2,397 children of school age living in the areas with different levels of or without iodine deficiency has been carried out. An increased frequency of cases with IQ not more than 80-85 scores was observed in iodine deficient areas. Iodine deficiency was a cause of clinically diagnosed borderline development delay only in 7% of children. Attention deficit syndrome (without hyperactivity) and anxiety-depressive disorders as well as asthenic symptoms were observed most frequently. Basing on the literature data and own observations, the author suggests a hypothesis on the pathogenetic basis of these disorders.