Due to a lack of controlled studies on HIV prevention interventions among Spanish adolescents, COMPAS, a five-session behavioral intervention, was developed and tested on Spanish adolescents aged 15-18. Participants included 827 adolescents from central, east and north Spain. Six hundred and seven students (M = 15.71 years) received the intervention. The control group consisted of 220 students (M = 15.78 years). The authors used self-report measures at two points in time to assess changes in HIV knowledge, HIV attitudes, perceived norms, and condom use intentions. Compared to the control group, the intervention group demonstrated improved outcomes with regard to HIV knowledge (d = 0.93) and HIV attitudes (d = 0.37), and maintained high levels of condom use intentions. The intervention's impact was greater in females and adolescents who were not sexually active. The findings suggest that COMPAS is an acceptable and feasible school intervention for reducing sexual risk among Spanish adolescents.