In the 19th century, the incidence of neonatal conjunctivitis varied between 1 and 14% in Europe, and the disease was a main cause of blindness at that time. Since then the epidemiology of ophthalmia neonatorum (ON) has changed and Chlamydia trachomatis is more frequent than Neisseria gonorrhoeae. Both are still very common causes of ON in the developing world. ON can not be differentiated clinically as to the etiology, but Intracellular Gram Negative Diplococci (IGND) on a Gram stain of an eye smear has an excellent validity and further differentiation can be made using microbiological cultures. All cases of presumed gonococcal conjunctivitis must be treated with effective systemic antibiotics. Systemic treatment with penicillin can still be used in areas where the percentage of beta-lactamase producing strains of gonococci is very low. For other areas a single dose of ceftriaxone intramuscular combined with saline eye washes is the treatment of choice. Chlamydial ON necessitates also systemic treatment with erythromycin. Parents of infants with gonococcal or chlamydia ON also need to be examined and treated. Prevention of gonococcal and chlamydial disease can be done following 3 strategies: antenatal diagnosis and treatment of maternal infections or disinfection of the infants eyes at birth or adequate treatment of infants and parents as soon as a ON has been diagnosed. Crédé's eye prophylaxis with silver nitrate has become a controversial issue, because of concern about the occurrence of chemical conjunctivitis and its ineffectiveness against infections with C. trachomatis.(ABSTRACT TRUNCATED AT 250 WORDS)