Infections of the conjunctiva are frequent in the neonatal period. While Neisseria gonorrhoea and chemical agents were considered as the main etiologies of ophtalmiae neonatorum in the past, Chlamydia trachomatis is today a major cause of neonatal conjunctivitis. Thus in a study of 180 uni-or bilateral neonatal conjunctivitis the authors found a prevalence of Chlamydia trachomatis infection of 41%. The importance of the etiological diagnosis of neonatal conjunctivitis is emphasized, in order to define a specific treatment. Etiological diagnosis of Chlamydia trachomatis infection is based upon immunofluorescence and molecular diagnosis techniques (PCR, LCR). Prevention of neonatal Chlamydia trachomatis conjunctivitis relies upon screening and treatment of Chlamydia trachomatis infections in pregnant women and their partners. Treatment requires oral macrolides, the topical treatment being ineffective.