BACKGROUND. Chlamydia trachomatis is the most common sexually transmitted pathogen in adults, which at delivery may be transmitted from mother to child and cause conjunctivitis and pneumonia. In the Netherlands, prenatal chlamydial screening and treatment of pregnant women is not routine practice. The contribution of C trachomatis to neonatal ophthalmic disease has not been studied in the Netherlands and remains unclear. METHODS. At the Sophia Children's Hospital and Rotterdam Eye Hospital, 2 cohorts of infants <3 months of age presenting with conjunctivitis were studied, 1 retrospectively (July 1996 to July 2001) and 1 prospectively (September 2001 to September 2002). Laboratory diagnosis was based on bacterial culture and polymerase chain reaction for C trachomatis. RESULTS. C trachomatis was detected in 27 (64%) of 42 retrospectively studied infants and 14 (61%) of 23 prospectively studied infants. Mucopurulent discharge was present in 35 (95%) of 37, swelling of the eyes in 27 (73%) of 37, conjunctival erythema in 24 (65%) of 37, respiratory symptoms in 14 (38%) of 37, and feeding problems in 5 (14%) of 37 infants respectively. Before microbiological diagnosis, general practitioners prescribed antichlamydial antibiotics locally to 5 (12%) of 41 and systemically to 4 (10%) of 41 infants who tested positive for chlamydia, and ophthalmologists prescribed to 21 (51%) of 41 and 7 (17%) of 41, respectively. CONCLUSIONS. C trachomatis was the major cause of bacterial conjunctivitis in this population. Clinically, differentiation from other pathogens was not possible. Many infants who tested positive for chlamydia did not receive appropriate antibiotic treatment. Copyright