A cross-sectional study assessed the extent to which indices of social structure, including family socio-economic status (SES), social deprivation, gender and educational/lifestyle aspirations correlated with adolescent condom use and added to the predictive utility of a theory of planned behaviour model. Analyses of survey data from 824 sexually active 16-year-olds (505 women and 319 men) tested three hypotheses. Firstly, social structure measures will correlate with behaviour-specific cognitions that predict condom use. Secondly, cognition measures will not fully mediate the effects of social structural indices and thirdly, the effects of cognitions on condom use will be moderated by social structure indices. All three hypotheses were supported. SES, gender and aspirations accounted for between 2 and 7% of the variance in behaviour-specific cognitions predicting condom use. Aspirations explained a further 4% of the variance in condom use, controlling for cognition effects. Mother's SES and gender added an additional 5%, controlling for aspirations. Overall, including significant moderation effects, of social structure indices increased the variance explained from 20.5% (for cognition measures alone) to 31%. These data indicate that social structure measures should to be investigated in addition to cognitions when modelling antecedents of behaviour, including condom use.