Features of expression of differentiation markers of peripheral blood lymphocytes were studied by flow cytofluorimetry in combination with clinical manifestations in 30 adult patients (12 men and 18 women, mean age 37.5±12.3 years) with the established diagnosis of сommon variable immunodeficiency (CVID). The examination of patients was carried out in the period of obvious absence of infectious and inflammatory diseases. It was found that the dominant immunophenotype in adult patients with СVID is an increase in the blood content of T cytotoxic lymphocytes (CD3+CD8+) with high expression of activation markers HLA- DR+ and CD38+ and a decrease in isotype-switched B lymphocytes IgD-27+ (in almost 100% of the examined individuals). The maximum degree of increase in the number of T killers was observed in patients with a low level of B lymphocytes (CD19+ less than 6%, p = 0.005) and a minimum concentration of IgG in the blood serum (less than 2 g/l, p = 0.02). The content of isotype-switched B cells correlated with the level of IgG, as well as the total concentration of serum immunoglobulins A, M and G (p = 0.02; p = 0.003). In adult СVID patients with the combined clinical phenotype “infectious syndrome + autoimmune disease”, the content of isotype-switched B lymphocytes, IgG and the total concentration of Ig in the blood is significantly lower (p = 0.04; p = 0.03 and p = 0.02), and activated T killers with HLA-DR+ and CD38+ expression are higher (p% = 0.01; rabs = 0.02 and p% = 0.004; rabs = 0.001, respectively) compared to patients with isolated infectious – inflammatory syndrome. We also found that among patients with the lowest number of isotype-switched IgD- 27+ B cells (less than 5%) and serum IgG concentration (less than 2 g/l), the incidence of lymphoproliferative syndrome is higher (p = 0.04 and p = 0.01, respectively). Thus, the low content of isotype-switched memory B lymphocytes in peripheral blood is most characteristic of patients with a more severe clinical phenotype of СVID.