With using a Raven test, technique of memorization of 10 words and Toulouse-Pieron test was studied cognitive state of adolescents with diffuse nontoxic goitre (DNG), taking into account the state of the thyroid system. It was shown that in the light iodine deficiency 44.7 % of adolescents with DNG have negative changes in the intellectual-mental sphere, mainly due to the disorders of attention, reduce the amount of short-term and long-term memory. Nearly in third of the surveyed adolescents with DNG diagnosed psychological signs of minimal brain dysfunction and decreased the operability. There is a strong relationship between the cognitive function and functional state of the thyroid system. Most negatively thyroid dysfunction affects on the amount of long-term memory and concentration of attention. The authors note the need of diagnostic and therapeutic algorithm for examination of children and adolescents with DNG, which would include not only the evaluation of the morphofunctional state of the thyroid gland, but also and evaluation of intellectual-mental sphere, the timely usage of a complex system of medical and psychological rehabilitation, aimed on supporting of cognitive function in patients with this pathology