Background. Recent studies have raised concern about efficacy of azithromycin for Chlamydia trachomatis infection. Research investigating new antibiotic regimens for chlamydia has been sparse, especially regimens that may reduce adherence difficulties with the recommended twice-daily doxycycline regimen.Methods.We conducted a randomized, double-blind, double-dummy, active-controlled, multicenter trial with the objective of evaluating the safety and efficacy of WC2031 (doxycycline hyclate delayed-release 200-mg tablet) orally once daily for 7 days versus Vibramycin (doxycycline hyclate capsule) 100 mg orally twice daily for 7 days for treatment of uncomplicated urogenital chlamydia. Men and nonpregnant women aged 19-45 years with a urogenital chlamydial diagnosis or a sexual partner with chlamydia were eligible. The primary outcome was microbial cure by nucleic acid amplification testing at day 28. Noninferiority of WC2031 was inferred if the lower limit of the 95 confidence interval (CI) of the difference in cure rates was >-10.Results.A total of 495 subjects were randomized. The modified intent-to-treat (mITT) population with evaluable efficacy consisted of 323 subjects. Baseline patient characteristics did not differ between the mITT groups. Microbial cure rates for WC2031 were 95.5 (95 CI, 92.3-98.8) versus 95.2 (95 CI, 92.0-98.4) for Vibramycin (95 CI for the difference in cure rates,-4.3 to 4.9). Types of adverse events were comparable. Nausea and vomiting occurred less frequently with WC2031 than with Vibramycin (13 vs 21 and 8 vs 12, respectively). Conclusions.WC2031 was noninferior to Vibramycin for uncomplicated urogenital chlamydia treatment, better tolerated, and demonstrated comparable safety. WC2031 could improve treatment adherence over twice-daily Vibramycin.Clinical Trials Registration. NCT01113931. © 2012 The Author.