Background: Competencies for adolescents with a healthy sexuality (COMPAS) is the only school-based sexual health promotion program in Spain that has been found to be as effective as an evidence-based intervention (¡Cuídate!) in the short term. This study’s aim was to compare data from a 12-month follow-up evaluation on the effects of COMPAS on adolescents’ sexual risks (knowledge, attitudes, perceived norms, sexual risk perception and intentions) and sexual behaviours (age of the first sex, consistent condom use and multiple partners) with an evidence-based intervention (¡Cuídate!) and a control group.

Methods: Eighteen schools from five provinces of Spain were randomly assigned to one of three conditions: COMPAS, ¡Cuídate! and a control group. The adolescents (N = 1563; 34% attrition) were evaluated 1 week before and after the program, and 1 year post-program implementation.

Results: We found that the COMPAS program was as effective as ¡Cuídate!, the evidence-based program, in increasing the adolescents’ knowledge about sexually transmitted infections and in fostering favourable attitudes about condom use and people living with HIV/AIDS. COMPAS was more effective than ¡Cuídate! in increasing the adolescents’ perceptions of their peer’s consistent condom use and the age delay of their first vaginal intercourse. However, it was less effective in maintaining the adolescents’ intentions to use condoms and in delaying the age of their first oral sex experience.

Conclusion: COMPAS was as effective as ¡Cuídate! in reducing sexual risk among adolescents.