Chlamydia trachomatis infection is the most commonly reported sexually transmitted disease (STD) in the United States, with the highest rates among adolescent females and young women. Approximately 5%-14% of routinely screened females aged 16-20 years and 3%-12% of women aged 20-24 years are infected with chlamydia. Because up to 70% of chlamydial infections in women are asymptomatic, routine screening and treatment of infected persons is essential to prevent pelvic inflammatory disease, infertility, ectopic pregnancy, and perinatal infections. Since the 1990s, CDC, the U.S. Preventive Services Task Force, and several clinical organizations have recommended routine screening for chlamydial infection for all sexually active women aged <26 years and for pregnant women of all ages. To evaluate rates of chlamydia screening among sexually active young females, CDC analyzed 1999-2001 data from the Health Plan Employer Data and Information Set (HEDIS) reported by commercial and Medicaid health insurance plans. This report summarizes the results of that analysis, which determined that screening rates were low despite slight increases in screening covered both by commercial and Medicaid plans during 1999-2001. Increased screening by health-care providers and coverage of screening by health plans will be necessary to reduce substantially the burden of chlamydial infection in the United States.