Objective: The objective of this study was to assess trends in Chlamydia trachomatis positivity and associated risk factors among detained female adolescents. Goal: The goal of this study was to determine trends in prevalence of chlamydia among detained female adolescents. Study Design: We retrospectively reviewed risk factor data and chlamydia results collected by providers during 1998-2002 at four large juvenile detention centers in Washington State that routinely screen female adolescents for C. trachomatis. Results: Of 3,593 tests, a total of 493 (13.7%) were positive for chlamydia. High chlamydia positivity was sustained throughout the 5-year period (range, 12.5-15.0%) with no statistically significant trends in positivity. Independent risk factors for chlamydial infection included report of more than one sex partner in the previous 60 days (adjusted odds ratio [OR] = 1.56, 95% confidence interval [CI] = 1.19-2.04) and previous chlamydial infection within 12 months (adjusted OR = 1.87, 95% CI = 1.45-2.40). Conclusions: Efforts are needed to promote chlamydia screening programs in juvenile detention centers because these sites have access to high-risk sexually active female adolescents.