Background. Agammaglobulinemia is a disease from the group of primary immune deficiencies with impaired antibodies production characterized by significant decrease or complete absence of B-cells. Due to the absence of pathogenetic treatment, severe bacterial lesions of various organs and tissues can develop, and they can lead to the patient death. Timely history taking and clinical and laboratory data analysis will allow to reveal this pathology early and start the therapy that can save patient’s life.Clinical case description. This article demonstrates clinical case of agammaglobulinemia late diagnosis with development of severe complications and reversal of clinical manifestations in response to pathogenetic therapy.Conclusion. Despite the disease onset in the second half-year period of life, the presence of recurrent purulent processes resistant to standard treatment and the significant decrease of all immunoglobulin levels, agammaglobulinemia was suspected only at preschool age. The outcomes were disabled patient, and considerable aggravation of the quality of life.