The objective of this work was to determine sexual knowledge, attitudes and practices in university students. An anonymous and previously tested questionnaire was applied to 328 students who entered the first year of the 8 careers of the Faculty of Medicine of University of Chile, in 1997. It was found that 25,5% of the students were coming from public schools, accept sexual relations when the occasion is given. 46,7% students less than 20 years old consider that premarital relations help to a better knowledge of the partner. 57,6% believe, that simultaneous orgasm is the central object in the sexual relation. The 42,6% of students less than 20 years has initiated sexual relations: 89,8% for women and 59,2% for men. This sexual initiation was with their steady boy or girl friend. The 73% had read or seenpornographic material. The 25,8% of this group had its sexual experience not with their steady boy or girl friend but with a different person, including strangers. In contrast nobody of the non exposed to pornography was sexually initiated with different person to girl or boy friends. In the other and, 43.1 % of those who had read or seen pornographic material declare oral or anal contacts versus 27.3% of those non exposed. The 62% of the students (95,7% men and 47,3 women) has practiced masturbation. The 40% showed insufficient level of knowledge in reproduction and sexuality, (achievement less than 60%.) These results, would explain their myths as: simultaneous orgasm, premarital relations thatimprove the relation of the couple, and risk practices such as oral or anal sex, in any occasion and with strangers. Therefore, the inclusion of sexual education for students who enter university is justified as primary prevention