BACKGROUND: Definitions of child sexual exploitation vary. Sexual exploitation violates children's rights and exposes them to mental and physical harm. There exist differences in views of behaviour that is considered exploitative, including transactional sex. This paper explores community perspectives on the extent to which transactional sex is considered exploitative. METHODS: In 2014, we conducted 19 focus group discussions and 44 in-depth interviews with young people and adults in two communities in Uganda. Participants were presented with vignettes describing sexual encounters between adolescent girls and young women and men to explore under what conditions participants considered the scenario to be exploitative and why. Interviews were conducted in Luganda using a semi-structured tool, audio recorded and transcribed verbatim. Analysis was thematic and complemented by constant comparison and deviant case analysis techniques. RESULTS: Definitions by multilateral, bilateral, and non-governmental organisations of the sexual exploitation of children shared similarities with community conceptualisations of wrong or unfair sex. Although in community conceptualisations there was no consensus on what constituted sexual exploitation, transactional sex was condemned to the extent to which it involved sex with a minor or misled a naïve or immature girl; involved lack of consent, particularly in relationships characterised by power differentials; or worsened the pre-existing status of the girl. Also relevant was the extent to which a man's intentions were considered inappropriate; the adolescent girl or young woman was considered vulnerable; and the adolescent girl or young woman was considered responsible for 'her situation'. CONCLUSIONS: Existing social norms that condemn sex with a minor or sex that involves deception, sexual coercion or misleading an immature girl, present opportunities to mobilise communities to protect adolescent girls and young women at risk. Any intervention must, however, be designed with full cognisance of the social and structural drivers that underlie transactional sex and limit adolescent girls' and young women's opportunities to provide for themselves without recourse to sexual relationships with men. Interventions must also be designed to recognise that girls in transactional sex relationships may not consider themselves as exploited, thus requiring engagement with them based on their own concerns, aspirations, and expectations.