Chlamydiae are microorganisms exhibiting characteristics intermediate between bacteria and viruses. Chlamydia is widespread in the natural world, intracellular parasites of people and animals. They are capable of independent reproduction, because they do not synthesize ATP, in its development cycle using the host cell metabolic pathways. The life cycle of these microorganisms is original, unique among bacteria and lasts from 24 to 48 hours. Chlamydia antigens consist of 4 groups: group-specific, species-specific, type-specific and subspecies-specific. The group of species-specific antigens consists of MOMP and heat shock proteins. C. trachomatis is a potent immunogen, stimulating the immune processes of microorganisms. In the course of C. trachomatis infection, the response mechanisms involved are: non-specific, specific, humoral and cellular. Chronic infection is characterized by maintenance of microorganisms in the host cell. Inflammation is formed in less time and with increased intensity and has a rapid immune response on the part of previously sensitized lymphocytes. C. trachomatis infections are the most common bacterial sexually-transmitted infections. It represents an important clinical problem for doctors in many areas of medicine such as dermatology, venereology, ophthalmology, gynecology and obstetrics, rheumatology and others. Chlamydial infections are important pathogens in medical practice, not only because they cause disease in various fields of medicine, but also because of the large proportion of the population suffering and exposed to these microbial infections. Chlamydial infections are characterized by multifocality and polymorphism changes. Chlamydia causes inflammation in the adult urethra and cervix with the possibility of serious complications, and can cause perinatal infections in infants.