Objective: To estimate the prevalence of Chlamydia trachomatis among first-year students at Paris 5. Method: Routine screening by PCR on a first-void urine sample, offered to first-year students at Paris 5 University who had been sexually active, during the mandatory medical examination. Results: A total of 1,018 subjects were included, with an overall prevalence of 1.0% [95% CI: 0.5–1.8]. This prevalence was 1.2% [95% CI: 0.4–2.6] among women and 0.8% [95% CI: 0.2–2.0] among men. Early onset of sexual activity is the main risk factor for Ct carriage, with a prevalence of 2.7% [95% CI: 0.9–6.2] when the first sexual intercourse occurred before age 16. Conclusion: The prevalence in this population is very low. (R.A.)