Objective of the research: to present the clinical and laboratory features of a child with a congenital deficiency of mannose-binding lectin (MBL). Materials and methods: DNA samples of 112 children suffering from frequent infectious diseases were analyzed by high-throughput sequencing (Illumina) using a panel including 338 genes associated with the development of primary immunodeficiencies. A search for pathogenic alleles of MBL2 was performed. A homozygous mutation in the MBL2 gene was detected in one of 112 examined patients, heterozygous carriage of the pathogenic MBL2 allele in two children. The story of a child with a homozygous defect of this gene is presented. The role of MSL deficiency in the development of a recurrent course of a nasopharyngeal infection caused by group A streptococcus, the formation of a chronic disease of the tonsils and adenoids is demonstrated.