Factors that make adolescents a high-risk group for HIV infection are patterns of adolescent sexual activity, the age of initiation of first intercourse, current contraceptive practices among teenagers, and the choice of sexual partners. The high rates of venereal diseases and anatomic and physiologic considerations also have a bearing on adolescents' vulnerability to HIV infection. Although adolescents are not significantly involved in IV drug use, they are at risk of being infected through sexual activity with the high percentage of young adults involved in IV drug use. Adolescents are a potentially high-risk group for HIV infection, and they should be targeted with primary prevention programs. 8 figures and 19 references.