Neonatal conjunctivitis associated with Chlamydia trachomatis has been known since the beginning of the century. Isolation of chlamydiae in eggs, in conjunctivitis of newborns, and from the cervix of their mothers was achieved in the late 1950s. In volunteers, inoculations of ocular and genital strains caused conjunctivitis. Recent studies have shown that incidence figures of chlamydial conjunctivitis in infants are 0.5% to 4%, depending on the prevalence of genital infections by C. trachomatis in the pregnant women in the population studied. Younger women are more at risk. Recurrent, chronic infection and late sequelae may occur unless neonatal chlamydial infection, which is often multifocal, is effectively treated. Serious sequelae of chlamydial infection include pneumonia, which may develop in infants, and post-partum salpingitis, which may occur in infected mothers.