Sexually transmitted infections and unplanned pregnancy among adolescents are important public health issues that can be tackled through the implementation of effective education strategies. Previous studies have documented the importance and effectiveness of parents as primary educators for their adolescents. A qualitative study based on grounded theory was undertaken in five different public high schools in Mexico and 33 interviews were carried out (18 parents and 15 first-year students). The primary prevention message that parents transmit to their adolescent children is abstinence. Prevention messages that include condom use and emergency contraception are scarce or absent. Promoting safer sexual behaviors among adolescents in Mexico is of critical importance. Nevertheless, the cultural scenario in the country is dictated mainly by a Catholic morality, which makes it difficult for parents to accept the possibility of their children being sexually active. Hence, the transmission of concrete information on the use of contraceptives is limited. Therefore, the challenge is to develop strategies that promote early and constant dialogue about sexuality between parents and children, respecting moral values within the family, but at the same time favoring clear and precise information about modern prevention practices. (Contains 2 tables.)