Objectives - To estimate the prevalence of Chlamydia trachomatis (Ct) infection in the French population, to assess the feasibility of a proposed at-home self-testing program, and to identify risk factors associated with Ct infection. Methods - The Survey on Sexuality in France (CSF) is a national survey of a random sample of the population aged 18–68 years conducted by telephone in 2006. Screening for Ct infection using home self-collection was offered to a subsample of individuals aged 18 to 44 (NatChla). The sample was weighted to account for the sampling design and then adjusted to represent the French population. Risk factors were identified among 18- to 29-year-olds using multivariate logistic regression. Results - A total of 2,580 people were tested (52% of those eligible). Among those aged 18 to 44, prevalence was 1.4% among men and 1.6% among women. This prevalence is higher among 18- to 29-year-olds (men: 2.5% [95% CI: 1.2–5.0], women: 3.2% [95% CI: 2.0–5.3]). The risk factor common to all 18- to 29-year-olds is having recently had a casual partner. Other risk factors identified for men include residing in the Île-de-France region or having recently had a new partner, and for women, having had more than two partners in the past year, same-sex partners, and having no formal education. Conclusions - NatChla has identified the risk factors that help define the populations to be screened as a priority. (R.A.)