The objective of the present study was to elucidate the structural and functional mechanisms underlying disturbances of the protective nasolaryngeal barrier with special reference to the following histological and immunohistochemical characteristics of the pharyngeal tonsils (CD4, CD20, CD68, IgA, P53, BCL2, Ki67, TGF-beta) in the children aged 3-6 years and presenting with complicated (n=20) or uncomplicated (n=20) chronic adenoiditis (CA). It was shown that adenoids of the patients with complicated chronic adenoiditis less frequently exhibit markers of active inflammation, such as hyperemia, intraepithelial infiltration, and hemosiderophages. Also, they have the smaller mean area of lymphoid follicles and the number of functional intrafollicular macrophages suggesting impaired immunological reactivity. Lymphoid follicles of the pharyngeal tonsils in the children with uncomplicated chronic adenoiditis show up enhanced density of B-lymphocytes (CD20) and CD69-positive cells which may suggest functional tension. However, density of IgA-producing lymphocytes responsible for the protection of nasolaryngeal mucosa is identical in the patients with complicated and uncomplicated chronic adenoiditis. Taken together with the decreased number of T-helpers (CG4), this finding indicates the compromised immunological response in the children with this pathology. It is concluded that the structural characteristics of pharyngeal tonsils revealed in the present study may provide a basis for the disturbances of congenital and adaptive immunity; moreover, they can serve as the predictors of complications of chronic adenoiditis.