Chlamydia trachomatis infection is the most prevalent sexually transmitted disease in developed countries today. It produces a number of oculogenital syndromes in adults as well as conjunctivitis and pneumonitis in infants. However, the most important sequelae are infertility, ectopic pregnancy, and chronic pelvic pain in women. Available diagnostic tests including culture are less than 100% sensitive but may be of considerable value in detecting asymptomatically infected individuals. Antichlamydial therapy is usually effective and should be given empirically to individuals whose presentation places them at high risk for infection.