The paper presents current knowledge about the clinical course, diagnostic and treatment of chlamydial infections in the neonatal period. In the neonatal period, infections caused by Chlamydia trachomatis are in the majority of maternal origin. Chlamydia mother to child transmission occurs during vaginal birth. It can also occur but rarely, during caesarean section after premature rupture of membranes. Chlamydia trachomatis infection of the genitourinary system in pregnancy increases the danger of intrauterine growth restriction and foetal death. It rises the perinatal morbidity of foetuses and newborns and increases the risk of premature deliveries. Chlamydia trachomatis infection in newborns manifests as conjunctivitis and ophthalmia and less commonly as pharyngitis and otitis media. Erythromycin is applied in prophylaxis and treatment of Chlamydia infections.