Background: Chlamydia trachomatis (CT) is a sexually transmitted infection having repercussions on reproductive health and impact on the fotus. Our goal was to estimate the prevalence of and risk factors for CT in young parturient women in Brazil. Methods: A national cross-sectional study of parturient women, aged 15 to 24 years, attending Brazilian public hospitals was performed in 2009. Participants answered a questionnaire including demographic, behavioral, and clinical data. A sample of urine was collected and screened for CT and Neisseria gonorrhoeae (NG), using polymerase chain reaction COBAS Amplicor CT/NG (Roche Molecular Systems, Branchburg, NJ). Results: A total of 2400 women were selected and 2071 (86.3%) participated in the study. Mean age was 20.2 years (standard deviation = 2.7). Prevalence rates of CT and NG were 9.8% (95% confidence interval [CI]: 8.5-11.1) and 1.0% (95% CI: 0.6%-1.4%), respectively. Four percent of women infected with CT also had NG infection. CT associated factors were: being younger (15-19 years old) (odds ratio [OR] = 1.6 [95% CI: 1.15-2.17]); first sexual intercourse before 15 years of age (OR = 1.4 [95% CI: 1.04-6.24]); having more than 1 sexual partner in lifetime (OR = 1.6 [95% CI: 1.13-2.26]); Pap smear screening more than 1 year (OR = 1.5 [95% CI: 1.08-2.05]); and NG infection (OR = 7.6 [95% CI: 3.05-19.08]).