The objective of this study is to design and evaluate an internet-based educational strategy to prevent sexual risk behaviors in Mexican adolescents. Methods: A field trial with one intervention and one comparison group, with ex-ante and ex-post measurements will be conducted in 2 public secondary schools. Adolescents between 14 and 15 years of age will participate. The intervention will be conducted in one school and the other school will serve as a comparison group, where investigators will observe the usual sexual education that the school provides. The intervention will be delivered through an internet web page; it includes four educational sessions that will be provided during a four-week period. The follow up will last three-months. The information on the study variables will be obtained through an internet-based self-applied questionnaire and collected on three occasions: when the adolescents enters to the study (baseline), once intervention is completed (at one month) and after three months of follow-up (at fourth month).