High levels of adolescent pregnancy and child marriage rates in low- and middle-income countries is an issue of concern to many stakeholders, including in Zambia where almost one-third of women give birth before age 18. The aim of this paper is to explore and analyse social norms concerning adolescents' sexual behaviour within the context of an intervention trial in rural communities in southern Zambia. It is based on a qualitative study applying individual interviews, focus group discussions and participatory research methods. We apply the distinction between injunctive and descriptive norms to demonstrate that adolescent girls are caught between conflicting norms. Injunctive norms express that premarital sex, contraceptive use, and discussions about sex between adults and youths are socially condemned. At the same time poor girls are reported to feel pressure towards having sexual relations for the economic benefits such relations can bring, and this practice is considered so common that it amounts to a descriptive norm. Norms and structural conditions combine to create a disabling and disempowering environment for adolescent sexual and reproductive health, which limits girls' agency and exposes them to unwanted pregnancies.