Chlamydia trachomatis infection is the most common bacterial sexually transmitted disease (STD) in the United States, with more than 2.8 million new cases estimated to occur each year. During 2007, approximately 1.1 million cases of chlamydia were reported to CDC; more than half of these were in females aged 15-25 years. Untreated chlamydia can progress to pelvic inflammatory disease (PID), infertility, ectopic pregnancy, and chronic pelvic pain. In 1989, the U.S. Preventive Services Task Force (USPSTF) recommended routine chlamydia screening of sexually active young women. To evaluate the rates of chlamydia screening among sexually active young females, CDC analyzed data reported by commercial and Medicaid health plans to the Healthcare Effectiveness Data and Information Set (HEDIS) during 2000-2007. The percentage of enrolled sexually active females who were screened for chlamydia was estimated for each of 41 states that had at least five health plans reporting HEDIS chlamydia screening data and for four U.S. geographic regions. Nationally, the annual screening rate increased from 25.3% in 2000 to 43.6% in 2006, and then decreased slightly to 41.6% in 2007. The regional rate of chlamydia screening in 2007 was highest in the Northeast (45.5%) and lowest in the South (37.3%). Increased screening by health-care providers is necessary to reduce the burden of chlamydial infection in the United States.