Chlamydia trachomatis is among the most prevalent of sexually transmitted diseases and causes serious sequelae, especially in women. A major difficulty facing the clinician has been the effective treatment of patients with chlamydial infections, since existing drugs require 7 or more days of multidose therapy, and hence considerable commitment from the patient. Many patients, especially those who are minimally symptomatic or asymptomatic, are likely to be noncompliant when given such multiple day regimens and thus may fail therapy. Azithromycin is an azalide antibiotic that has a minimum inhibitory concentration against C. trachomatis of between 0.03 and 0.25 mg/L, as well as good in vitro activity against other sexually transmitted pathogens that are often present concurrently. Azithromycin also achieves high intracellular concentrations, which may be beneficial in eradicating Chlamydia, an obligate intracellular pathogen. More importantly, azithromycin has high tissue bioavailability and a tissue half-life of between 2 and 4 days. These pharmacokinetic properties imply that the dosing period for azithromycin can be greatly reduced while still achieving high antimicrobial activity at sites of infection. Clinical experience to date shows that a single 1 g oral dose of azithromycin is as effective as a standard 7-day twice daily regimen of doxycycline and more effective than 7 days of ciprofloxacin in eradicating uncomplicated chlamydial genital infections. As such, azithromycin is the first single-dose therapy for the treatment of urethritis and cervicitis due to C. trachomatis. Single-dose therapy for chlamydial infection, which could be administered under supervision in the clinic, would be a significant advance in the management and public health control of chlamydial infections.