Chlamydia trachomatis is a pathogen with an intracellular developmental cycle. Sexually transmitted infection with serotypes D to K can lead to cervicitis, endometritis, salpingitis and urethritis, however, symptoms are commonly mild. Newborns of mothers with cervical infection or colonisation can acquire inclusion conjunctivitis and atypical pneumonia. An efficient prophylaxis is not available so far. Antimicrobial therapy should be initiated as soon as chlamydial infection is confirmed, e.g. with tetracyclines or erythromycin. Partner treatment is mandatory.