Introduction. An urgent problem in many countries of the world is the growth of comorbid diseases and conditions associated with the pathological use of the Internet, including functional somatic disorders, which include asthenic syndrome.Purpose of the study. To study the frequency of occurrence of asthenic syndrome schoolchildren with different online behavior during the coronavirus pandemic.Materials and methods. The method of random sampling was used to examine 1 148 adolescents at the age of 11–18 years, of which 535 (46.6%) were boys and 613 (53.4%) were girls. The frequency of occurrence was analyzed in the entire sample of the surveyed, as well as in the comparison groups, formed by gender: 1 gr. – boys (n = 535), 2 gr. – girls (n = 613), age: 1 gr. – 11–14 years old (m + d) (n = 837) and 2 gr. – 15–18 years old (m + d) (n = 311), type of online behavior: 1 gr. – with adaptive use of the Internet, 2 gr. – with maladaptive internet use, 3 gr. – with pathological use of the Internet and type of Internet addiction.Results. The frequency of adaptive use of the Internet was 37.0%, with maladaptive – 49.9% and with pathological – 13.1% of the total sample of the surveyed. The content structure of the online behavior of Tuvan schoolchildren includes the presence of a game Internet addiction in 4.4% of the surveyed, dependence on social networks – in 12.5%, mixed IА – in 2.4% and undifferentiated IА – in 5.0%. The frequency of asthenic syndrome is 12.2% of all surveyed.Conclusion. A more pronounced association of asthenic syndrome in schoolchildren with maladaptive online behavior indicates the negative impact of the computer and the Internet on the body and justifies the need for a personalized approach to these contingents.