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teria are not always clear, particularly in settings where chlamydia prevalence is low—as is the case for some family planning providers. The increasing integration of STD services into family planning settings requires the development and evaluation of risk-assessment tools that are appropriate for these populations.7 When resources allocated for the prevention and control of chlamydial disease were expanded in 1993,8 the Centers for Disease Control and Prevention (CDC) issued revised guidelines for selective screening for chlamydial infection in women.9 However, the performance of these guidelines in predicting chlamydial infection has not been compared in population-based studies with that of criteria based on young age or behavioral risk. In this article, to make such a comparison, we use data from the Region X Chlamydia Project, which has coordinated chlamydia screening for approximately 500 family planning and STD clinics in Alaska, Idaho, Oregon and Washington (U. S. Public Health Service Region X) since 1988. As part of the project, more than 600,000 women have been tested for chlamydia over that time, with an associated dramatic decline in chlamydia prevalence in the Pacific Northwest.10 Three periods of universal screening were conducted among women visiting health providers serving populations with low and moderate levels of chlamydia prevalence. Among these women, we retrospectively compared the performance of the CDC’s selective screening criteria Jeanne M. Marrazzo is an instructor in the Department of Medicine, University of Washington, Seattle; David Fine is associate regional manager of the Center for Health Training, Seattle; Connie L. Celum is associate professor in the Department of Medicine, University of Washington, Seattle; Susan DeLisle is infertility prevention activity coordinater with the Centers for Disease Control and Prevention (CDC), Atlanta, Ga.; and H. Hunter Handsfield is a professor in the Department of Medicine, University of Washington, Seattle, and is director of the Sexually Transmitted Diseases (STD) Control Program at the Seattle–King County Department of Public Health. The research on which this article is based was supported in part by the National Institute of Allergies and Infectious Diseases under STD/AIDS Research Training Grant T32 AI-07140 and by the CDC. The authors thank Debra J. Mosure for ongoing assistance with the Region X Chlamydia Project and are grateful to the many participating clinics, providers and patients who made the study possible. Selective Screening for Chlamydial Infection In Women: A Comparison of Three Sets of Criteria