Purpose: to study infection prevalence by Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG), among adolescent and young women in a family planning outpatient clinic. Methods: a total of 230 women up to 24 years old and history of up to four sexual partners have been followed-up for 48 months, with urine collection to search CT and NG, by the polymerase chain reaction method at the 1st, 12nd, 24th, 36th and 48th months. The variables studied were age group, schooling, marital status, number of gestations, abortions and children alive, age at the onset of sexual life, previous and present use of condom, previous use of intrauterine device, number of sexual partners in the previous six months and follow-up time. Bivariate analysis of variables according to positive tests for CT and NG, and multiple analyses by logistic regression were done. Results: the ratio of infections by CT was 13.5% and by NG, 3%. Two women presented both tests as positive. 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