Immunodeficiency in the neonatal period is often recorded. Neutro- and lymphopenia of secondary genesis are detected in various infectious diseases of the ante-, intra- and postnatal period of infection. Primary immunodeficiency occurs due to genetic breakdown of the immune system and is included in the syndrome complexes of hereditary and chromosomal diseases. The clinic of immunodeficiency conditions does not have a specific picture, and is realized as a sluggish infectious disease, often leading to sepsis. Newborn children, especially premature infants, have a functionally immature immune system, do not form an adequate immune response when exposed to pathogens, which leads to rapid generalization of infectious diseases. An infectious process against the background of congenital immunodeficiency can lead to death. A clinical example of the development of a generalized infectious process with secondary immunodeficiency clearly shows the difficulty of curating patients with a fatal outcome.