In developed countries, Chlamydia trachomatis (CT) is found on the cervix of the uterus in 2-8% of pregnant women. Two thirds of neonates from infected mothers are contaminated at delivery at the level of ocular, respiratory and digestive mucosal surfaces. This infection is responsible for 40% of neonatal conjunctivitis and afebrile pneumonitis in the second and third month after birth. In older children and adolescents, CT is responsible for genital infections contracted by venereal contact. The treatment requires taking a macrolide orally for 15 days. Prevention requires the detection of high-risk women, and hygiene in sexual intercourse.