Physiological shrinking (involution) of the pharyngeal tonsil occurs in adolescence due to the changes in the hormonal profile of the body. However, adenoids occur not only in adolescents but in adults as well. To clarify the etiology of the lymphoepithelial pharyngeal ring tonsils hypertrophy, the authors examined 46 children. Among them, there were 22 boys aged 13–18 years and 24 girls aged 12–18 years. According to the results obtained, the share of adolescents with concurrent endocrine diseases among all the adolescents operated on for adenoids was 40%, but only 10% subjected to regular check-up of an endocrinologist. 35% of children were obese, 25% had vegetative-vascular dysfunction manifestations. The tests for infections showed the persisting streptococcal infection in 25% of adolescents with high concentration of AS(L)O (300–800 units). 75% of patients had EBV and CMV. 25% of children had serological and molecular genetic markers, which indicate an active infectious process. It should be specifically noted that 1 child had HIV infection. The share of adolescents with allergic rhinitis and allergic diseases (atopic dermatitis, bronchial asthma) among all adolescents operated on for adenoids was 34%. Therefore, in 72.2% of cases, the adolescents had concurrent endocrine diseases or allergic rhinitis in combination with allergic diseases (atopic dermatitis, bronchial asthma), or persistent EBV, CMV or streptococcal infection, or a combination of these diseases (25%).