The most frequently seen type of infectious ophthalmia neonatorum, inclusion conjunctivitis, is caused by the organism Chlamydia trachomatis. This agent is known to be transmitted sexually. Until recently, the infections produced by C trachomatis were though to be relatively benign. Recent evidence, however, suggests that the organism may produce urethritis and epididymitis in the male; cervicitis, cervical erosions, salpingitis, and puerperal infections in the female; and prematurity and pneumonitis in the infant. An infant who develops ophthalmia neonatorum should be thoroughly evaluated for the presence of a chlamydial infection. In many instances the first evidence of chlamydial infection within the parents will be the development of inclusion conjunctivitis in their newborn infant. Family members of infants with inclusion conjunctivitis who manifest any evidence of clinical disease should be evaluated and treated with appropriate antibiotics.