After chlamydia became a nationally notifiable condition in the United States, reported case rates increased steadily, likely a result of more complete reporting, expanded screening efforts, and use of more sensitive diagnostic tests. Reported case rates of chlamydia are highest among young women, a consequence of high prevalence in this population (as evidenced by estimates from national population-based surveys) and of targeted screening efforts (current guidelines in the United States recommend screening for all sexually active females aged <25 years). However, after a decade of increasing reported case rates, case rates have recently declined among adolescent women aged 15–19 years: during 2001–2011, case rates increased 49.8% (2,327 to 3,485 per 100,000 females) and then decreased 15.1% during 2011–2014 (3,485 to 2,960 per 100,000 females). We explored possible reasons for decreases in chlamydia case rates among adolescent females using available national data and highlight how decreases in screening coverage among key populations may be impacting reported case rate trends.