Objectives - To determine the prevalence of Chlamydia trachomatis (Ct) urogenital infections among women seeking care at 24 Family Planning and Education Centers (CPEF) in Val-de-Marne, and to assess the feasibility of a protocol for routine screening and treatment. Method - From January to March 1999, 1,023 sexually active women under the age of 30 underwent endocervical and urethral swab testing. The samples were analyzed using gene amplification (Cobas Amplicor CT PCR, Roche). Results - The prevalence of Ct infection is 7.1% [95% CI: 5.6–8.7]. Risk factors independently associated with infection are: age under 25, country of birth in Africa or the Caribbean, a new sexual partner in the previous 12 months, and out-of-pocket healthcare costs. Conducting systematic screening among women under 25 years of age would involve testing 73% of the women in the study and corresponds to a screening sensitivity of 89%. Adding another criterion would result in testing nearly all patients. Conclusion - The dual endocervical and urethral swab was well accepted by patients. The high prevalence found in this population of young, economically vulnerable women justifies the implementation of a systematic screening program. (R.A.)