The proposed study is a single center (with multiple long-term YCFs) treatment trial of the CDC-recommended azithromycin regimen (1 gm PO once) for chlamydia in males residing in long-term gender-segregated YCFs. This study is designed primarily to determine the frequency of chlamydia treatment failure following azithromycin in males who do versus do not have urethral symptoms of urethral discharge and/or dysuria. Males age 12 to 21 years in good health (based on vital signs and provider's clinical evaluation documented in medical records) who are residing in long-term gender-segregated (not co-ed) YCFs (usual stay > 3 weeks) and who are identified as chlamydia-infected comprise the study population. The anticipated enrollment is 446 males with subject participation duration of 28 days and study duration of 4 years. The primary objective of the study is to assess the microbiological efficacy of azithromycin in uncomplicated Chlamydia trachomatis infection in males with versus without urethral symptoms in YCFs; in essence, this study will assess the frequency of chlamydia treatment failure to azithromycin at the Day 28 follow-up visit (Visit 2) in males with urethral symptoms compared to males without urethral symptoms. The secondary objective is to evaluate the association of laboratory findings (enrollment chlamydia load and OmpA genotype) and other participant characteristics (demographics, sexual behaviors, etc.) to chlamydia treatment failure in males after azithromycin treatment.