A survey was conducted among a sample of clinical laboratories to calculate the rates of positive test results for Chlamydia trachomatis (Ct) by age, sex, and type of healthcare setting. The aim of this survey was to obtain data to aid in decision-making regarding which healthcare settings should implement screening of asymptomatic individuals. Laboratories belonging to the Renachla surveillance network were contacted. Forty-four laboratories agreed to participate and provided information on 15,597 individuals who underwent a diagnostic test using direct identification. Records where certain variables (age, sex, information on the location of the referral, and test result) were incomplete were not included. Ultimately, the analysis focused on 8,879 genitourinary specimens collected from individuals over the age of 14 who had sought care at one of the following locations: private medical or gynecological practice, hospital gynecology clinic, maternity-obstetrics unit, venereal disease clinic (Dav), anonymous and free screening center (CDAG), family planning center (CPEF), and reproductive health center. Information regarding these 8,879 individuals was collected by 23 laboratories (12 private and 11 public) primarily in 2001. The positivity rate is the ratio of the number of individuals with at least one positive sample to the number of individuals tested via a genitourinary sample. A subject with multiple samples was counted only once. Among private and hospital-based gynecologists, the positivity rate decreases with age: it is over 5% among women under 19, around 3% among those aged 20–29, and drops sharply after age 29 (<2%). In family planning clinics and reproductive health centers, the positivity rate remains high up to age 29. In Davs, the rate is very high (>10%) up to age 24 for women and up to age 34 for men. In CDAGs, positivity rates are high (>7%) up to age 24 for women and at all ages for men. This study identified, for young people under 25, areas where the positivity rate is very high for both men and women (9–14% in DAVs and CDAGs) and areas where the positivity rate is high but at a lower level (4–5% among hospital and private gynecologists, in CPEFs, and in family planning clinics). Among general practitioners, the positivity rate among young people under 25 is 0% for women and 5.6% for men; however, no conclusions can be drawn due to the small sample size (52 women tested with no positive cases, 18 men tested with one positive case). This survey demonstrates that it is possible to conduct surveys of medical laboratories by collecting data on the age and sex of the tested individual and the location where the test was ordered, particularly when computerization allows them to extract the requested data. The results of this survey support the recommendations of the National Agency for Health Accreditation and Evaluation (Anaes) proposing to implement in France systematic opportunistic screening for Ct-related urogenital infections in CPEFs, CDAGs, DAVs, and family planning centers, preferably among women under 25 and men under 30. (R.A.)