In Western industrialized countries, conjunctivitis caused by Chlamydia trachomatis is most prevalent in adults at about the age of 20 years. In the case of classical trachoma in developing countries, the highest incidence of active disease occurs in children between 2 and 5 years of age. Inclusion conjunctivitis in adults is usually an autoinfection, resulting from a concomitant genital chlamydial infection. By contrast, in endemic trachoma the infection is spread from eye to eye. Only rarely has a nongenital transmission of inclusion conjunctivitis been inferred, among medical personnel and after swimming-pool bathing. Neonates with inclusion blennorrhea also may transmit the infection to family members. Diagnosis relies on the demonstration of C. trachomatis recovered from infected eyes. Treating chlamydial eye infection in adults means controlling the concomitant genital infection as well. The recommended treatment is oral tetracycline or erythromycin.