Objectives: To review reported chlamydia infection trends in the U.S. military and identify reasons for differences. Methods: Defense Medical Surveillance System 2000-2008 reports for nondeployed, active duty members were studied. Incidence, rate ratios, and confi dence intervals were generated. Age- and gender-specific rates were compared with US national rates. Screening and reporting policies and procedures were reviewed. Results: Overall incidence was 922 cases per 100,000 person-years, with considerable service variability (392-1,431 cases per 100,000 person-years in the Navy and Army, respectively). Navy-Marine Corps rates increased more than 2 fold in 2008. Rates were higher among women, minorities, and members under 25 years. Military rates exceeded national rates. Conclusions: The 2008 increase in Navy-Marine Corps rates may be due to the implementation of web-based reporting. Demographic differences were consistent with published reports. The civilian-military disparity may refl ect higher percentages of military at-risk women screened.