Recent data indicate that the worldwide rate of HIV infection in adolescents is steadily increasing. Internationally, more than 7000 youths between 15 and 24 years of age are infected with HIV daily, resulting in more than 2.5 million new infections annually. Almost two thirds (1.7 million) of these new infections occur in Africa. Estimates in 2000 showed that the number of South Africans between 15 and 49 years of age infected with HIV was 4.7 million. This number equates to a prevalence rate of 15.4% in those younger than 20 years. Adolescents form an important target group not only for preventative efforts but also for HIV vaccine trials. This article focuses on the social and psychological factors that affect adolescent decision making by considering adolescent risk-taking behaviors, problems associated with predicting adolescent behavior, peer relationships and decision making, sexual disinhibition, and the role of family relationships in adolescent decision making.