Concerns about the impact of risk compensation on advances in biomedical human immunodeficiency virus (HIV) prevention technologies have been documented. We conducted an exploratory qualitative study using focus group discussions with young South African men and women (aged 18 to 24 years) to explore perceptions of risk compensation with regard to a hypothetical posttrial HIV vaccine. During the discussions, participants expressed their disquiet about the potential for risk compensation and the manner in which this might manifest among young people. Discussions specifically focused on reductions in condom use, an increase in multiple partners, and increased frequency of sex. The discussions also revealed contradictory feelings about HIV vaccines: appreciation for their development tempered by concerns about loss of control and undermining morality. Women were particularly concerned with the possibility of increased partner concurrency and infidelity. We suggest that concerns in HIV vaccine target populations about the impact of possible risk compensation be incorporated into strategies for vaccine introduction once vaccines move from the hypothetical to reality.