This article presents the National Peer Education Program, a sex education model which is being implemented by the Fundação Portuguesa A Comunidade Contra a Sida (Portuguese Foundation The Community Against AIDS) in Portuguese schools. Based on the epidemiological data and a review on the theoretical and empirical background to peer education, this text presents and discusses the main stages of intervention, and raises topical and controversial issues in the area of Sex Education, which continue to present a challenge for contemporary Education .