Introduction: Chlamydia trachomatis is the most common agent of sexually transmitted infections. In pregnant women it can cause premature delivery. In newborns the clinical manifestation are pneumonia and conjunctivitis. Aim: The aim of the study was to estimate the perinatal transmission of Chlamydia trachomatis and the prevalence of neonatal complications. Material and methods: The study included 82 mothers with delivery <34 weeks of gestation and 100 of their newborns. All patients were hospitalized at the Poznan University of Medical Sciences Gynecology and Obstetrics Hospital between 2004 and 2009. Polymerase chain reaction (PCR) method in AMPLICOR CT/NG test was used for the detection of Chlamydia trachomatis infection. Results: Chlamydia trachomatis was identified in 8 pregnant women among 82 tested patients (10%) and in 6 neonates. Perinatal transmission was 75%. All infected infants developed respiratory disorders. Five of them needed respiratory support such as nCPAP or mechanical ventilation. Three newborns presented apneic spells. Conclusions: Asymptomatic chlamydial infection is frequently detected in women with preterm delivery. There is high risk of perinatal transmission of the infection from the mother to the newborn, which leads to perinatal complications such as neonatal pneumonia which in preterm infants can develop just after the delivery and give rise to life-threatening respiratory disorders.