Teenagers are the vulnerable group of contracting HIV because of changes in the reproductiveorgans are more mature in adolescents, causing a boost sexual arousal and stronger in her teens.The purpose of this study was to describe the knowledge and attitudes of adolescents in the preventionof HIV/AIDS. The method used descriptive, a population of this research is all student on second gradeof catholic high school students of Diponegoro Blitar were 219, the samples size was 65 students usingsystematic random sampling techniques, and use of a questionnaire. The results showed knowledge inthe prevention of adolescent HIV/AIDS some 66% (43 students) had good knowledge. The attitude ofyoung people in the prevention of HIV/AIDS some 52% (34 students) had a positive attitude, because allstudent have given health promotion about HIV/AIDS. Recommendations of this study are expected toconduct health promotion officer of health promotion, education materials that expand the knowledgeand attitudes of adolescents can develop better and will affect the health status of adolescents.