Background: Adolescents are vulnerable to sexually transmitted infections (STIs) and unplanned pregnancy. Prevention measures and assistance are of significant public health importance in this population. Objective: The objective of this study was to identify demographic, behavioral, and clinical factors for STIs and to determine the prevalence of Chlamydia trachomatis infection (CT) among female adolescents in Vito´ria, Brazil. Methods: We performed a cross-sectional study among female adolescents (15–19 years) served by the Health Family Program. Participants were screened for CT and Neisseria gonorrhoeae (GC) using ligase chain reaction applied to urine and answered a face-to-face questionnaire to assess demographic, behavioral, and clinical factors. All participants and their parents signed the informed consent. Results: Four hundred sixty-four young women were sampled. The prevalence of CT was 8.9% (95% confidence interval [CI], 6.5–11.9%) overall. Among sexually active women, CT and gonorrhea prevalence were 12.2 (95% CI, 9.4–17.0%) and 1.9% (95% CI, 1.1–2.7%), respectively. Previously diagnosed STI was reported by 12.8%. Women who reported regular condom use and having condoms at home were significantly less likely to have CT, and having never purchased condoms was significantly associated with a positive CT result. Conclusion: A high prevalence of CT was found in this population, and behavioral risk was high despite readily available STI prevention information. Women who reported positive condom use behaviors were less likely to have CT. These results demonstrate the need for ongoing STI prevention activities, including STI screening and continued successful risk reduction activities such as condom use to further decrease CT and other STI among adolescents.Funding for this study was provided by FACITEC (Fundo de Apoio a Ciência e Tecnologia), Vitória Municipality, UNESCO: Projeto 914 BRA 3016, 5° termo aditivo acordo Brasil-França and from the NIH/Fogarty Centers ICOHORTA Grant (1 D43 TW05799–03).