Immunoglobulins are among the most important factors of humoral immunity, providing protection against all types of pathogens and most tumor cells. Under normal conditions, the humoral immune response to most antigens results in the synthesis of antibodies of all four IgG subclasses. One of the most probable concepts suggests that the antibody response is prolonged, with the gradual recruitment of new classes and subclasses of immunoglobulins as the previous ones fail to effectively eliminate the antigen. According to this concept, the primary response to an antigen begins with IgM, followed by IgG3 (and/or IgE). If the antigen is not eliminated, the synthesis of IgG1 and IgG2 is activated. If this is insufficient, the production of IgG4 begins, which is a marker of the chronicity of the immune response or an indicator of the multiple immune responses to the same antigen. IgG4-associated diseases were identified as a distinct group of autoimmune pathologies only at the beginning of the 21st century, when in 2001 Hamano et al. identified a link between certain diseases and elevated levels of IgG4 production. This article examines the diagnostic criteria, clinical features, and current treatment principles for IgG4-associated diseases. Key words: immunoglobulin G4, sclerosing cholangitis, IgG4-associated diseases, diagnostics, treatment.