Chlamydia trachomatis is the most common bacterial pathogen causing sexually transmitted infections in Dutch adults. As prenatal screening for C trachomatis and treatment of pregnant women is not routine practice in The Netherlands, perinatal transmission of C trachomatis may therefore occur. The presence of C trachomatis in infants less than 6 months of age who presented with respiratory complaints to the Erasmus MC-Sophia hospital was evaluated. Respiratory specimens, primarily nasopharyngeal swabs, were tested for C trachomatis, respiratory viruses and Mycoplasma pneumoniae using PCR, viral isolation in cell cultures and direct immunofluorescence. C trachomatis respiratory tract infection was confirmed to be relatively common with detection in 10 of 148 (7%) infants tested. C trachomatis had not been tested for by the attending physicians, but was the second most frequently detected respiratory pathogen after human Respiratory Syncitial Virus, which was found in 41 (28%) infants.