Background: AIDS (Acquired Immunodeficiency Syndrome) is a collection of symptoms or diseases caused by a decrease in the immune system from the body due to infection from the HIV (Human Immunodeficiency Virus) which belongs to the retroviridae family. Teenagers themselves are vulnerable to HIV/AIDS. The right and precise knowledge of HIV and AIDS is important in HIV prevention efforts in adolescents. Method: This research is a descriptive research with cross-sectional design. The sample population of this study was grade XII senior high school students of the 2020/2021 at Methodist – 2 Medan by sampling total sampling. This study was analyzed univariately to look at the descriptive images. Result: From the results of this study, it has obtained that the knowledge level of students grade XII Methodist - 2 Medan had good knowledge about HIV / AIDS with the number of 144 people (70.6%). Conclusion: From this study, it was found that the level of knowledge about HIV/AIDS was mostly in a good category.