BACKGROUND Although most teenagers know the consequences of the exercise of sexuality without protection, it is surprising that a percentage will be pregnant yet despite having received prior information. OBJECTIVE Explore some of the knowledge, beliefs and attitudes about sexuality in pregnant adolescents younger than 17 years. METHODS Exploratory, observational, cross-sectional and retrospective study with non-experimental design of a single specimen consisting of a questionnaire with the following questions: at what age did you have your first boyfriend?, at what age did you have your first sexual relationship?, did you receive information about sexuality?, do you think that the information that you received from sexuality was good, regular or bad?, did the information you received prepared you for the start of your sex life?, how was your first sexual relationship?, what were the reasons to start sexual activity?, where did you have your first sexual relation? RESULTS 158 patients with average age of 15.6 participated in the sample years and schooling of 8.8 years. Menarche occurred to the 11.5 years, one year later they had boyfriend and two years later the first intercourse. The 59.6% had a history that her mother also became pregnant as a teenager. The 94.3% received information about sexuality; 58.2% considered it good and 38.6% regular. Sexual life was started by curiosity and desire in 67.1% and referred it as pleasant and very enjoyable 80.9% of girls; 39.5% of them think that the bride and groom should not have no sexual relationship. CONCLUSIONS Younger than 17 years pregnant teens enjoy their first sexual experience, they reach it by curiosity and desire, but they exercise it without protection, despite having knowledge of the consequences.