One of the worst HIV/AIDS epidemics in the world is occurring in South Africa, where heterosexual exposure is the main mode of HIV transmission. Young people 15–24 years of age, particularly women, account for a large share of new infections. Accordingly, there is an urgent need for behavior-change interventions to reduce the incidence of HIV among adolescents in South Africa. However, there are few such interventions with proven efficacy for South African adolescents, especially young adolescents. A recent cluster-randomized controlled trial of the ‘Let Us Protect Our Future!’ HIV/STD risk-reduction intervention for Grade 6 South African adolescents (mean age = 12.4 years) found significant decreases in self-reported sexual risk behaviors compared with a control intervention. This article describes the intervention, the use of the social cognitive theory and the reasoned action approach to develop the intervention, how formative research informed its development and the acceptability of the intervention. Challenges in designing and implementing HIV/STD risk-reduction interventions for young adolescents in sub-Saharan Africa are discussed.