In recent years, ample evidence has accumulated indicating the advantage of sexual health programs that incorporate a gender perspective. However, to our knowledge, there are no empirical studies on the influence of sexist attitudes on the effectiveness of sex education programs. This study aims to demonstrate that sexism has a negative impact on the results obtained by sex education programs in the prevention of sexual risks through two studies. Study 1 tests whether a sex education program differs in effectiveness based on the level of Ambivalent Sexism (ASI) and Sexual Double Standard (DSS). The sample was composed by 293 Basque-speaking adolescents from nine secondary schools in the Basque Country (M = 15.56, SD = 0.63, range: 15-17). Study 2 analyses whether introducing training aimed at reducing levels of sexism achieves that the sexual education program obtains similar results in young people with high and low sexism -ASI, DSS and the Inventory of Distorted Thoughts on Women and Violence (IDTWV) -. The sample is made up of 340 Basque-speaking adolescents from eight secondary schools in the Basque Country (M = 15.54, SD = 0.57, range: 15-17). Results point to the relevance of including gender perspective in sexual education programs aimed towards reducing sexism, especially sexual double standards, in order to increase its effectiveness in the prevention of sexual risks.