Chlamydia trachomatis infections are the most frequent bacterial sexually transmitted diseases in the United States, with an estimated 4 million cases occurring annually. The mainstay of treatment for chlamydial infections has been the tetracyclines. Doxycycline, comparable in cost to tetracycline and with a less frequent dosage schedule, is the drug of first choice. Erythromycins are the drugs of choice for infections in pregnant women, nursing mothers, infants, children, and adults unable to tolerate tetracyclines. beta-Lactam antibiotics have had variable efficacy against C. trachomatis infections, although recent studies suggest that amoxicillin may be an effective alternative for C. trachomatis infection during pregnancy. Quinolones are currently being tested and may be used in alternative regimens in the future. The effectiveness of current antimicrobial regimens in preventing long-term complications of chlamydial infections should be determined in research studies.